Ch32

FIGURE 163 Washington navel sweet orange shoots. Left: Right: stubbornaffected shoot with short internodes, pale green, palmate leaves with yellow tips (Latif El Dileimi orchard, Rachidiya, Iraq)

FIGURE 164 Pink, seedless Thompson grapefruit tree on Cleopatra mandarin rootstock, with dieback and fruit of different sizes ranging from small green to fully matured. Foliage was yellowish because of high pH. Some leaves were mottled because of stubborn agent. Indeed, Spiroplasma citri was cultured from this tree (Deir Alla Experiment Station, Jordan)

FIGURE 165 Upper figure: acorn-shaped Washington navel sweet orange fruit, characteristic of stubborn. Peduncular (upper) end of fruit is thickened and has a coarse texture; styler (lower) end is smooth (Citrus mother tree plantation, Akhelia-Paphos, Cyprus). Lower figure: cross section through stubborn-affected, acornshaped Washington navel sweet orange fruit showing thick albedo at peduncular (upper) end and thin albedo at styler (lower) end (Heguy orchard, Rharb, Morocco)

FIGURE 166 Ripening of normal fruit (sweet orange). Stylar (lower) end is already orange while peduncular (upper) end is still green. Degreening begins at styler end (Algeria)

FIGURE 167 Ripening of stubborn-affected fruit (Washington navel sweet orange). Degreening begins at peduncular (upper) end which turns orange, while styler (lower) end is still green. This phenomenon is called "colour inversion" (Toukatly orchard, Saleh Basatine, Syria)

FIGURE 168 Sectioned Mahali sweet orange fruits from stubborn-affected tree. Note that fruits are lopsided and have a curved axis (columella). Seeds are aborted. Some fruits have mummified styler ends. Spiroplasma citri was cultured from the peduncular ends of the columellae (Behadli orchard, Kerbala, Iraq)

FIGURE 169 Lopsided, stubborn-affected, young grapefruit. Note that part of the albedo is coloured blue. Blue albedo, as shown here, is often found on fruit (sweet orange, grapefruit) from stubborn-affected trees, but is not specific to stubborn (Resvan orchard, Bab Anar, Fars province, Iran)

FIGURE 170 Salsola kali is extremely common from Morocco to Iran. It grows particularly well along the seashores of Morocco, Syria and Cyprus (Amrit-Tartus, Syria)

FIGURE 171 Salsola kali is an annual plant. It turns brown and dies in the winter, as shown here on the seashore near Curium in Cyprus

FIGURE 172 Close-up of a dead Salsola kali shoot. Note prickle-like tips of floral leaves (Petra ton Romiou, Cyprus)

FIGURE 173 In the winter, under the influence of strong winds, dead Salsola kali plants break off easily and tumble over the ground, hence the name "tumbleweed" (Seashore near Ormidhia, Cyprus)

FIGURE 174 Salsola kali growing as a weed in a citrus nursery. Being a major host plant of the leafhopper vectors of Spiroplasma citri, the presence of this weed in a nursery explains the high rate of S. citri transmission to citrus that is observed in such nurseries (New citrus nursery, El Annadeh, Syria)

FIGURE 175 Periwinkle (Catharanthus roseus) plants. Left: healthy plant. Right and middle: Spiroplasma citri-infected plants. Plant at right was grown at 25°C and shows essentially feat yellows. Middle plant was grown at 32°C and shows S. citri-induced lethal wilting in addition to feat yellows (INRA Bordeaux)

FIGURE 176 Periwinkle (Catharanthus roseus) plant naturally infected with Spiroplasma citri which has developed lethal wilting (see Figure 175) during the hot summer months (Beni Mellal, Tadla, Morocco)

FIGURE 177 Twenty-six-year-old greening affected navel sweet orange tree on unrecorded rootstock (probably rough lemon). Presence of greening bacterium in phloem was confirmed by electron microscopy (Awadle Elmi-M.A. Hersi orchard, Arapsiyo area, Hargeisa, Somalia)

FIGURE 178 Twenty-six- year-old greening-affected Jaffa sweet orange tree on unrecorded rootstock (probably rough lemon). Presence of greening bacterium in phloem was confirmed by electron microscopy (Awadle Elmi- M.A. Hersi orchard, Arapsiyo area, Hargeisa, Somalia)

FIGURE 179 Close-up of greeningaffected navel sweet orange tree showing dieback, sparse foliage with zinc-deficiency patterns and off-season flowering. Presence of greening bacterium in phloem was confirmed by electron microscopy (Awadle Elmi-M.A. Hersi orchard, Arapsiyo area, Hargeisa, Somalia)

FIGURE 180 Leaves of sweet orange showing mottling symptoms characteristic of greening disease. Note also vein corking (Awadle Elmi-M.A. Hersi orchard, Arapsiyo area, Hargeisa, Somalia)

FIGURE 181 Citrus collection at Aussfera farm, Ta'izz (northern Yemen). Most trees in this collection were affected by greening and advice was given to eradicate the trees (see Figure 182)

FIGURE 182 Citrus collection at Aussfera farm after heavy pruning. Trees were not pulled out as advised (see Figure 181) but heavily pruned. The many young, tender shoots induced by this treatment are used by Trioza erytreae, the psyllid vector of greening, as a source of food. Thus, heavy pruning involuntarily favours transmission of the greening agent

FIGURE 183 Three-year-old Washington navel sweet orange trees. Left: normal tree. Right: stunted, greening-affected tree; infection with the greening bacterium (confirmed by electron microscopy) was probably through natural transmission by Trioza erytreae psyllids (Aussfera farm, Ta'izz, northern Yemen)

FIGURE 184 Sweet orange leaves showing leaf mottle characteristic of greening (Aussfera farm, Ta'izz, northern Yemen)

FIGURE 185 Greening-effected, small-fruited acid lime seedling tree. Upper, yellow part of tree shows symptoms of greening (confirmed by electron microscopy) (Barakani, Ta'izz region, northern Yemen)

FIGURE 186 Close-up of greening-affected, small-fruited acid limo tree. Normal shoot: lower left corner in figure (Barakani, Ta'izz region, northern Yemen)

FIGURE 187 Small-fruited acid lime leaves showing feat mottle characteristic of greening; the greening BLO was detected by electron microscopy in this tree. Three leaves show, in addition, bumps specific to Trioza erytreae (see also Figures 189 to 193) (Barakani, Ta'izz region, northern Yemen)

FIGURE 188 Eggs of Trioza erytreae along the midrib and the margins of a lemon feat (Ihalidanana, Madagascar)

FIGURE 189 Lower tree of a sour orange feat with many small, concave depressions produced by the developing nymphs of Trioza erytreae (see also Figure 192). Some of the depressions are empty, others are still occupied by nymphs. On the upper face of the feat many protuberances or bumps can be seen, which correspond to the concave depressions of the lower face (see also Figures 190 and 193) (Ahmed Hydan orchard, Mukayras, southern Yemen)

FIGURE 190 Upper facet of sour orange leaves with many bumps caused by the development of Trioza erytreae nymphs on the lower face. Leaf on left Is that In Figure 189 (Ahmed Hydan orchard, Mukayras, southern Yemen)

FIGURE 191 Trioza erytreaeinduced bumps on Clementine feat (Hammam Ali, northern Yemen)

FIGURE 192 Trioza erytreae-induced depressions on lower face of lemon leaves (Aussfera farm, Ta'izz, northern Yemen)

FIGURE 193 Bumps on the upper face of the leaves in Figure 192. Depressions on the lower face are seen as bumps on the upper face

FIGURE 194 Heterogeneous fruit from greening-affected, 12-year-old Valencia late sweet orange tree. Note colour inversion on some fruit (Nasser Al Kahr Shuti orchard Dinahem, Al Baida, northern Yemen)

FIGURE 195 Fruit in Figure 194, when sectioned, show curved fruit axes and seed abortion

FIGURE 196 Stunted, greeningaffected mandarin tree on sour orange rootstock. Presence of greening bacterium was confirmed by electron microscopy (King Faizal orchard, Taif, Saudi Arabia)

FIGURE 197 Stunted, greeningaffected sweet orange tree on sour orange rootstock. Presence of bacterium was confirmed by electron microscopy. Tree was also affected by gummy bark. Cambial face of bark revealed conspicuous pinholing on both sweet orange and sour orange bark (see Figure 198). Tree was negating for tristeza virus by ELISA (Bakhit Addaussari orchard, Bishah, Saudi Arabia)

FIGURE 198 Inner (cambial) face of piece of bark removed across bud-union of stunted, greening-affected affected sweet orange tree on sour orange rootstock in Figure 208 and showing conspicuous pinholing above and below budunion line

FIGURE 199 Ten-year-old mandarin orchard destroyed by greening (Maid Wazen orchard, Turabah, Saudi Arabia)

FIGURE 200 Close up of one of the mandarin trees of Maid Wazen orchard (Figure 199). Presence of greening bacterium in leaf phloem was confirmed by electron microscopy (see Figure 10)

FIGURE 201 Fruit from mandarin tree in Figure 200 with many brownish, aborted seeds

FIGURE 202 Zinc-deficiency symptoms and some mottle on leaves from greening- affected mandarin tree in Figure 200

FIGURE 203 Mottle and some zinc-deficiency symptoms on mandarin leaves from the Abdelhahmid Al Saigh orchard in Wadi Nahman (Mecca area, Saudi Arabia). The leaves were collected on trees initially imported from Jordan. The trees became infected in Saudi Arabia after having been planted, as the Al Saigh orchard is heavily infested by Diaphorina citri, the psyllid vector of the greening BLO, and Jordan is tree of both greening and its vector

FIGURE 204 Greening-affected mandarin tree similar to that in Figure 200. Strong suckers have grown out of the sour orange rootstock of this greening-affected tree and have overgrown the dying mandarin scion (Maid Wazen orchard, Turabah, Saudi Arabia)

FIGURE 205 Dying, greeningaffected mandarin tree in the Bishah area (Abdelaziz Abdula orchard, Saudi Arabia)

FIGURE 206 Foreground: Iwo dying mandarin trees affected by both greening and mild cachexia. Background: greening affected lime tree. This figure illustrates well that lime trees are less susceptible to greening than mandarin trees. It is in this area that the two psyllid vectors of greening occur together in the same orchards (Brehim Khaibar, Khamis Mushait area, Saudi Arabia)

FIGURE 207 Leaves of small-fruited acid lime tree showing galls induced by Trioza erytreae, the African psylild vector of greening. These galls look like bumps on the upper face of the leaves (upper row of leaves) and depressions (in which the nymphs have lived) on the lower face (lower row of leaves) (Brehim Khaibar, Khamis Mushait area, Saudi Arabia)

FIGURE 208 Foliage of three year-old Washington navel tree showing zincdeficiency symptoms, most probably due to greening. Indeed, the greening BLO was detected by electron microscopy in this tree, and many leaves showed galls induced by Trioza erytreae, the African psyllid vector of greening (Agricultural Experiment Station, Fayfa, Saudi Arabia)

FIGURE 209 Shoot from threeyear-old Washington navel tree in Figure 208 showing Trioza erytreae. induced depressions or galls on lower leaves and zinc deficiency symptoms on upper leaves

FIGURE 210 Adults of Diaphorina citri feeding on lower face of a small-fruited acid lime leaf (Abdula Abbouche orchard, Taif, Saudi Arabia). Insert: arrow points at a Diaphorina citri psyllid feeding on the lower face of a sour orange feat (Tarnab Agricultural Research Institute, Peshawar, Pakistan)

FIGURE 211 Many nymphs and a few adults of Diaphorina citri feeding on small-fruited acid lime leaves. Leaves are very misshapen and are covered with honeydew (Ode Gamdi orchard, Turabah, Saudi Arabia)

FIGURE 212 Diaphorina citri induced damage on small-fruited acid lime foliage. Leaf curling and distortion (Mohamed Yousset Atouwem orchard, Khurmah, Saudi Arabia)

FIGURE 213 Diaphorina citri induced damage on small-fruited acid lime tree: leaf drop, dieback, leaf curling (Maid Wazen orchard, Turabah, Saudi Arabia)

FIGURE 214 Greening- induced leaf mottle on small-fruited acid lime leaves. Presence of greening bacterium in phloem was confirmed by electron microscopy (El Gharif, Khurmah, Saudi Arabia)

FIGURE 215 Declining Kinnow mandarin orchard near Lahore (Pakistan). Insert shows fruit sectioned from this orchard; note the many aborted seeds

FIGURE 216 Declining Bloodred sweet orange tree on rough lemon rootstock with greening-like aspect (Horticultural Research Station, Sahiwal, Pakistan)

FIGURE 217 Right half of tree Is still normal. Left half is affected by greening-like symptoms (Horticultural Research Station, Sahiwal, Pakistan)

FIGURE 218 Murraya paniculata (Aurantioldeae), a widely used ornamental citroid, is a preferred host of Diaphorina citri, the Asian psyllid vector of the greening BLO. It can be used successfully to rear a citri in the glasshouse (Wat Phra Keow, Bangkok, Thailand)

FIGURE 219 Dodder (Cuscuta campestris) strands connect greening affected sweet orange seedling to periwinkle (Catharanthus roseus) for transmission of the greening bacterium from citrus to periwinkle (INRA, Bordeaux)

FIGURE 220 Leaf symptoms of periwinkle (Catharanthus roseus) infected with the greening bacterium (Poona strain) (INRA, Bordeaux)

FIGURE 221 Longitudinal thin section through midvein of greening-affected periwinkle (Catharanthus roseus) leaf. MAs developed against the BLO associated with greening have been used to detect the BLO by immunofluorescence. When viewed under ultraviolet light, the BLOs present in the phloem are detected by a greenish-yellow fluorescence on a red background of plant tissue (INRA, Bordeaux)

FIGURE 222 Typical phytophthora footrot lesion on grapefruit tree on sour orange rootstock with budunion too close to the soil (Folco orchard, Mogadishu, Somalia)

FIGURE 223 Balady sweet orange tree on sour orange rootstock showing streaks of gum on the scratched part of the trunk, and phytophthora lesions on either side. Gum streaks in the sweet orange bark show the tree is affected by gummy bark. Phytophthora infection is caused by the bud-union being too close to the soil (Mussa Bahardin orchard, Nyertete, the Sudan)

FIGURE 224 Young sweet orange tree on sour orange rootstock with soil piled around trunk, covering up bud-union line (All Al Emir orchard, Al Raju, Marib, northern Yemen)

FIGURE 225 Sweet orange tree with soil piled around trunk and covering up bud-union line (Al Radod orchard, Say'un-Tarim, southern Yemen)

FIGURE 226 Upper view: grapefruit tree on sour orange rootstock with soil piled around the trunk, covering bud-union (Government orchard, Baled, Somalia). Lower view: in Iraq, soil removed when cleaning irrigation ditches is piled around citrus trunks (Dorah, Iraq)

FIGURE 227 In this young citrus orchard, trees are planted at the right- angle crossings of irrigation furrows. To prevent the trunks of the trees from being in direct contact with water, soil will undoubtedly be piled up against the trees, thus favouring quick phytophthora damage (Saad Al Sudeyri orchard, Al Khelil, Medina region, Saudi Arabia)

FIGURE 228 Young lemon tree on sour orange rootstock. Removal of soil from around trunk showed bud-union to be buried below soil level, with lemon scion in contact with soil. Removal of bark shows severe and extended phytophthora lesion on the lemon scion above bud-union, but no attack on the resistant sour orange rootstock (Fahama, Iraq)

FIGURE 229 A row of young lemon trees on sour orange rootstock. Trees were planted too deep, with bud-unions buried below soil level and trees began to show phytophthora lesions above soil level. Soil was removed from around the trunks and used to build circular levees to protect the trunks from irrigation waters (Government nursery, Ibb, northern Yemen)

FIGURE 230 One ot the young lemon trees on sour orange rootstock in Figure 229, showing severe phytophthora lesions extending high above bud-union

FIGURE 231 Circular soil levee protects trunk from irrigation water (M. Abdullah Aboussita orchard, Awbarkadle, Hargeisa, Somalia)

FIGURE 232 Five year-old, mal secco affected lemon tree on sour orange rootstock (Slang Experiment Station, Jable, Syria)

FIGURE 233 Left: mal secco-affected Limoneira A8 lemon shoot. Right: normal shoot (Finike, Turkey)

FIGURE 234 The hyphae of Deuterophoma tracheiphila (Petri), the causal fungus of mal secco, stain the wood red, as shown here in an Ortanique tangor shoot (Lanitis orchard, Limassol, Cyprus)

FIGURE 235 Woody cylinders of Limoneira A8 shoots after removal of bark. Left: normal wood. Right: pinkish-red stained wood from a mal secco-affected shoot (Finike, Turkey)

FIGURE 236 Rio Grande gummosis-affected, 20-year-old grapefruit tree on sour orange rootstock. Note profuse exudations of amberbrown gum through cracks or lesions of the bark (see Figures 244 and 245). The gum runs down the trunk and accumulates in stalactite-like masses (Central Agricultural Research Station, Afgoi, Somalia)

FIGURE 237 Rio Grande gummosis affected grapefruit tree on sour orange rootstock (AFMET farm, Giohar, Somalia)

FIGURE 238 Rio Grande gummosis-affected grapefruit tree on sour orange rootstock (Quarantine orchard, Afgoi, Somalia)

FIGURE 239 Rio Grande gummosis-affected, 20-year-old grapefruit tree on sour orange rootstock (Central Agricultural Research Station, Afgoi, Somalia)

FIGURE 240 Rio Grande gummosis-affected, 20-yearold grapefruit tree on sour orange rootstock with young, active, gum-producing lesions and old, inactive, nonproducing (dry) lesions with exposed wood at the centre (Central Agricultural Research Station, Afgoi, Somalia)

FIGURE 241 Rio Grand gummosis-affected, 20-year-old grapefruit tree with several old, inactive, dry lesions with bark scaling on the rims or lips and exposed wood at the centre (Central Agricultural Research Station, Afgoi, Somalia)

FIGURE 242 Close up of an old, inactive lesion on Rio Grande gummosis-affected sweet orange trunk (Mauza, northern Yemen)

FIGURE 243 Grapefruit tree showing bark scaling associated with Rio Grande gummosis (Central Agricultural Research Station, Afgoi, Somalia)

FIGURE 244 Rio Grande gummosis-affected Marsh seedless grapefruit tree. Gum oozes out through vertical cracks of the bark (upper view). The cracks are revealed by cutting off the outer layers of bark (lower view, left) (Mustapha Osman orchard, Atbara, the Sudan)

FIGURE 245 The trunk of the tree in Figure 244. When a piece of bark is further removed to expose the wood (upper view, left) abundant gum, located between bark and wood, flows out of the open wound. Removal of the outer layers of wood (lower view, left) shows that there are also gum pockets within the wood

FIGURE 246 Rio Grande gummosisaffected Jaffa sweet orange tree showing leaf drop. Here, defoliation is essentially due to a high salt problem, but expression of Rio Grande gummosis seems to be favoured by high concentrations of chlorides in the soil (Kharalambos Hadji Georgiou orchard, Alaminos.Latouros, Cyprus)

FIGURE 247 Crosssection of a branch from Rio Grande gummosis-affected Jaffa sweet orange tree on sour orange rootstock in Figure 246. Note ambencoloured gum oozing out from between bark and wood

FIGURES 248 and 249 Upper (Figure 248) and lower (Figure 249) faces of a small-fruited acid lime leaf with canker lesions due to the bacterium Xanthomonas campestris pv. citri A canker lesion has raised, corky, craterlike eruptions on both faces of the leaf. Citrus scab and, more particularly, sour orange scab due to the fungus Elsinoe fawcetti also have raised pustules, but only on the Involved face of the leaf (Said Ben Rachid Kilbani orchard, Homania, Ibri, Oman)

FIGURE 250 Close-up of advanced canker lesions on upper (left) and lower (right) faces of a small-fruited acid lime leaf. Note yellow hald around lesions (Said Salem Al Wahebi orchard, Salalah, Oman)

FIGURE 251 Cork-like canker pustules on twigs of small-fruited acid lime (Said Ben Rachid Kilbani orchard, Homania, Ibri, Oman)

FIGURE 252 Sweet province orange tree with symptoms of autumn blast (Jiroft Development Organization, Kerman, Iran)

FIGURE 253 Close-up of autumn blast on sweet orange twig. Note abundant gumming at arrows (Mansurya, Iraq)

FIGURE 254 Autumn blast on Valencia late sweet orange (Mudia nursery, southern Yemen)

FIGURE 255 Upper: symptoms of salt injury on Jaffa sweet orange leaves. Note yellowing and "burning" of leaf tip and margins. Excess of chloride, sodium, potassium, magnesium, ammonium, lithium and other elements produces these symptoms. Here excess of ClNa is Involved (Had; Dalan orchard, Horohadle, Hargeisa, Somalia) Lower: excess boron induces similar effects. In addition, brownish resinous gum spots are present on lower surface of leaf (Al Shumaymri orchard, Unaizah region, Saudi Arabia)

FIGURE 256 Symptoms of boron excess on upper tree of lemon leaves. Note tip and marginal yellowing and/or mottling. See also Figure 255 (Hindya, Iraq)

FIGURE 257 Lower face of the lemon leaves in Figure 256. Note brownish, resinous gum spots or pustules characteristic of boron excess. See also Figure 255

FIGURE 258 Old-line lemon tree on sour orange rootstock with shell bark-like scaling of the outer layers of bark above bud-union. Shell bark is a genetic affection. The outer bark dries out and cracks into vertical strips. The inner bark and cambium remain intact, and the affected outer bark is sloughed after healing occurs (Mauza, northern Yemen)

FIGURE 259 Bearss lime tree on sour orange rootstock showing bark cracking. Such longitudinal cracks are normal in vigorously growing trees. Wood- pocket of Persian (Tahiti, Bearss) lime in Florida is somewhat similar but affected trees show leaf blotch in addition (Government orchard, Zalingei, the Sudan)

FIGURE 260 Trunk of a stunted, five-yearold Musambi sweet orange tree on Seville Kimb. sour orange rootstock. Removal of a piece of bark across bud-union reveals conspicuous stem pitting and some inverse stem pining on the sour orange wood, with corresponding pegging and pinholing on the cambial face of sour orange bark (see Figure 261 ) (Horticultural Research Station, Sahiwal, Pakistan)

FIGURE 261 Inner (cambial) tree of bark removed from trunk in Figure $0 showing pegging, pinholing and staining with gum. like material on sour orange bark only. Tree indexed negative by ELISA for tristeza virus

FIGURE 262 Two views of the cambial face of a piece of bark removed across the bud-union of a mandarin tree on an unrecorded rootstock. Pegging and gumming of mandarin bark are characteristic of cachexia. Pegs on the unrecorded rootstock bark cannot be traced back to a given disease as the nature of rootstock is not known. However, in this orchard rough lemon has been identified as the rootstock of a sweet orange tree (see caption to Figure 76). If the rootstock were rough lemon, the pegs on its bark as well as some bark gumming below the bud-union could be due to gummy bark (Al Sagifa Abduraba Golan orchard, Harib, northern Yemen)

FIGURE 263 Trunk of mandarin tree on unrecorded rootstock (tree A). Mandarin scion shows severe stem pining symptoms of cachexia; note also cracks in the bark. Rootstock is symptomless. See also Figure 265 (M. Wabrane orchard, El Jorba area, Najran, Saudi Arabia)

FIGURE 264 Trunk of mandarin tree on unrecorded rootstock (tree B). Mandarin scion is symptomless, but there is severe stem pitting and bark cracking on rootstock. See also Figure 265 (M. Wabrane orchard, El Jorba area, Najran, Saudi Arabia)

FIGURE 265 Inner face of bark from the two mandarin trees in Figures 263 (tree A) and 264 (tree B). Middle: piece of bark from tree A showing pegs on mandarin bark; rootstock bark is symptomless. Left and right: two pieces of bark from tree S showing pegs on unrecorded rootstock bark; mandarin scion bark is symptomless. Symptoms on rootstock of tree B cannot be traced back to a given disease as nature of rootstock is not known. They could be those of gummy bark it the rootstock were rough lemon. They cannot be due to the cachexia agent as there are no symptoms on the cachexia-susceptible mandarin scion. Cracks in the bark resemble those exocortis on sweet lime or Dorshapo sweet lemon

FIGURE 266 Inner face of a piece of bark removed across bud-union of a mandarin tree on unrecorded rootstock. Here, there is severe bark pegging and gumming on the mandarin scion indicating presence of cachexia agent, but also pegging on the rootstock bark similar to that of tree in Figure 264; rootstock bark shows also cracking (M. Wabrane orchard, El Jorba area, Najran, Saudi Arabia)

FIGURE 267 Stunted, ten-year-old sweet orange tree on unrecorded rootstock. Rootstock bark shows splitting; see Figure 268 (All Abdel Jalil orchard, Najran, Saudi Arabia)

FIGURE 268 Trunk of sweet orange tree in Figure 267 showing splitting and cracking of rootstock bark. There is also stem pitting on rootstock

FIGURE 269 Trunk of sweet orange tree on unrecorded rootstock. Note pitting on rootstock stem (right) and corresponding pegging on inner face of rootstock bark. Cracks on rootstock bark are similar to those in Figures 268 and 270 (Khaled Al Sudeyri orchard, Najran, Saudi Arabia)

FIGURE 270 The bark cracking and stem pitting observed on the unrecorded rootstocks of trees in Figures 268 and 269 show up even on young sweet orange trees as seen here (AIi Aboussak orchard, Najran, Saudi Arabia)

FIGURE 271 Stunted sweet orange tree on sweet lime (Emir Meteb orchard, Buraidah region, Saudi Arabia)

FIGURE 272 Trunk of tree in Figure 271. Nob poor union, splitting of rootstock bark (exocortis?) and staining of rootstock stem immediately below bud-union

FIGURE 273 Trunk of Balady mandarin tree on sour orange rootstock. The bark has been scraped to show cachexia symptoms: streaks of gum in the mandarin bark but not in the sour orange bark (Shreita orchard, Besnada, Syria)

FIGURE 274 Trunk of tree in Figure 273 after removal of a strip of bark to show symptoms of cachexia. In the case shown here stem pitting is very mild while bark gumming is heavy

FIGURE 275 Psorosis young leaf symptoms of the vein-flecking type on young nursery sweet orange trees. See also Figures 93 to 97 (Government nursery, El Annadeh, Syria)

FIGURE 276 Scaly bark psorosis (psorosis A) on scion of Mandalina mandarin trees on sour orange rootstock (Ashrafie, Syria)

FIGURES 277 and 278 Symptoms of concave gum on two branches of a Washington navel sweet orange tree. As shown here, concave gum symptoms are of two types: broad concavities - concavity in Figure 278 is deeper than that in Figure 277; gum production, especially with cultivars such as Washington navel sweet orange and Orlando tangelo. Note the heavy gum production near the concavities (Hassad Kanaan orchard, Meterkie, Syria)

FIGURE 279 Severe symptoms of impietratura (pockets of gum in albedo) on grapefruit (Shreita orchard, Besnada, Syria)

FIGURE 280 Clementine tree on sour orange rootstock showing cachexia symptoms, immediately above the scraped bud-union zone: streaks of gum In the bark, small stem pits and corresponding pegs on bark (see Figure 281). The tree also shows cristacortis symptoms: the deep, narrow, longitudinal pits with corresponding pegs on bark (see Figure 281) (Ashrafie, Syria)

FIGURE 281 Inner (cambial) side of strip of bark removed from tree in Figure 280

FIGURE 282 Trunk of Mandalina mandarin tree on sour orange rootstock affected by cachexia and cristacortis. Cachexia is diagnosed on the basis of gum deposits in the mandarin bark (gumming is mild); stem pining above bud union line and in the top part of the trunk is due to the cristacortis agent. The bumpiness of the trunk above bud-union and higher up is typical of severe cristacortis stem pining (Ashrafie, Syria)

FIGURE 283 Close-up of bud-union part of trunk in Figure 282

FIGURE 284 Close-up of top part of trunk in Figure 282

FIGURE 285 Four-year-old Washington navel sweet orange trees (cultivar 141). Symptomless tree is on the left. Stubborn-affected tree (R4A27) on right became infected with S. citri through natural contamination. Tree was positive for S. citri by ELISA and the culture assay (Sweet orange mother tree plot, FAO project, El Annadeh, Syria)

FIGURE 286 Four-year-old Atwood navel sweet orange trees. Symptomless tree is on the left. Stubborn-affected tree (R3A7) on right became infected with Spiroplasma citri through natural contamination. Tree was positive for S. citri by ELISA and the culture assay (Sweet orange mother tree plot, FAO project, El Annadeh, Syria)

FIGURE 287 Four-year-old Marsh seedless grapefruit trees (cultivar 119). Symptomless tree is on the right. Stubbornaffected tree (R8A46) on left became infected with Spiroplasma citri through natural contamination. Tree was positive for S. citri by ELISA and the culture assay (Grapefruit mother tree plot, FAO project, El Annadeh, Syria)

FIGURE 288 Shoots from symptomless tree in Figure 287 are on left; shoots from stubborn-affected tree (R8A46) are on right

FIGURE 289 Four-year old Clementine trees (cultivar 88). Stubborn-affected tree Is in the middle and became infected with Spiroplasma citri through natural contamination. Tree was positive for S. citri by ELISA and the culture assay. Syrnptomless trees are on each side [Mandarin mother tree plot, FAO project, El Annadeh, Syria)

FIGURE 290 Tunnels covered with tine mesh screen tissue to grow nursery trees in the absence of leafhoppers (New citrus nursery, El Annadeh, Syria)

FIGURE 291 D-vac aspirator for capture of leafhoppers and other insects on plants and trees (Kassab area, Syria)

FIGURE 292 Periwinkle (Catharanthus roseus) plant (number 203) infected with Spiroplasma citri through natural contamination. Plant was positive for S. citri by ELISA and the culture assay (Nursery III, FAO project, El Annadeh, Syria)

FIGURE 293 Trunk of tree grafted on Citrus volkameriana rootstock. Note stem pitting and wood staining on rootstock. Vogel indexed the tree for cachexia on Parson's Special mandarin and found the tree tree of cachexia. Therefore the symptoms on C. volkameriana cannot be due to the cachexia agent. C volkameriana is tolerant of cachexia (Citrus Experiment Station, Jable, Syria)

FIGURE 294 Trunk of lemon tree grafted on Citrus volkameriana rootstock. In addition to the symptoms shown on rootstock in Figure 293, there seems to be bud-union incompatibility (Centre of Agriculture, Tartus, Syria)

FIGURE 295 Stubborn-affected Valencia late sweet orange tree on Cleopatra mandarin rootstock. Yellow foliage results from the joint effect of stubborn and high pH of soil. Spiroplasma citri was cultured from the columella of a fruit with colour inversion and seed abortion (see also Figure 164) (Deir Alla Experiment Station, Jordan)

FIGURE 296 Streaks of gum in scraped bark of cachexi-axyloporosis-affected Mandalina mandarin; no gum is present in the tolerant rootstock. The mandarin scion also showed concave gum-blind pocket symptoms (Deir Alla Experiment Station, Jordan)

FIGURE 297 Stunted Washington navel sweet orange tree on sour orange rootstock with severe bud-union crease (see Figure 298) (Deir Alla Experiment Station, Jordan)

FIGURE 298 Cambial side of piece of bark removed across bud-union of tree in Figure 297. Because of bud-union crease the piece of bark broke at the bud-union line while being removed from the trunk. Note tine pinholing below and more conspicuous pinholing above bud-union line. Bud-union crease is not a symptom of stubborn. Pinholing on the sour orange rootstock below bud-union line is a symptom associated with stubborn and tristeza but is not specific. It is open found on severely stressed trees. The tree in Figure 297 indexed negative for tristeza virus by ELISA and Spiroplasma citri could not be cultured from the tree

FIGURE 299 Stunted, cachexiaxyloporosis-affected Jaffa sweet orange tree on Citrus macrophylla rootstock. The symptoms of cachexia, stem pitting (Figure 300) and bark gumming (Figure 301) are seen on the cachexia-susceptible rootstock (Hamraniyah Experiment Station, United Arab Emirates)

FIGURE 300 Trunk of tree in Figure 299 with severe stem pitting on Citrus macrophylla rootstock, but no symptoms on tolerant sweet orange scion

FIGURE 301 Cambial side of piece of bark from trunk in Figure 300 with cachexia symptoms on rootstock bark: conspicuous pegs matching the pits in the stem (right) and gum in the outer layers of bark (left); no symptoms on scion bark

FIGURE 302 Shoots from a Washington navel sweet orange tree; leaves are palmate with blunt tips as a result of heat. In addition, the tips of some leaves are yellow, which suggests stubborn disease. Salt injury can also induce yellow tips (Hamraniyah Experiment Station, United Arab Emirates)

FIGURE 303 Washington navel sweet orange from in Figure 302. Fruit is lopsided; albedo is thick at peduncular end and thin at styler end. These symptoms are indicative of stubborn

FIGURE 304 Aborted seeds In a fruit from a Balady sweet orange tree with stubborn like symptoms (Masafi, United Arab Emirates)

FIGURE 305 Periwinkle (Catharanthus roseus) plant naturally infected with Spiroplasma citri as detected by electron microscopy. This plant was one of many periwinkles growing as ornamentals along Dubai creek, in Dubai town (United Arab Emirates)

FIGURE 306 Witches' broom from a smallfruited acid lime tree resulting probably from a bud mutation. Witches' brooms induced by the MLO of witches' broom disease of lime are very different (compare this figure with Figures 136 to 140) (All Bin Rogha orchard, Kalba area, United Arab Emirates)

FIGURE 307 Declining Kinnow mandarin tree of Pakistani origin showing severe dieback (Hamraniyah Experiment Station, United Arab Emirates)

FIGURE 308 Declining Eureka lemon trees of Californian origin on Citrus volkameriana rootstock. The cause of this decline is not known. It does not seem to be mal secco. Alternaria sp. was isolated from affected leaves (see Figure 309) (Hamraniyah Experiment Station, United Arab Emirates)

FIGURE 309 Leaves with necrotic zones from lemon tree in Figure 308. Alternaria sp. was isolated from the necrotic zones

FIGURE 310 Sunburn on Ruby blood grapefruit (Hamraniyah Experiment Station, United Arab Emirates)

FIGURE 311 Fine orchard of small-fruited acid lime trees (Sheik Sakar orchard, Kalba, United Arab Emirates)

FIGURE 312 Fine Lisbon lemon trees at the Dhaid Substation for Agricultural Development (Dhaid, United Arab Emirates)

FIGURE 313 Fine grapefruit trees in the fruit farm at Dibba (United Arab Emirates)

FIGURE 314 Chimera type variegation on leaves of Valencia late sweet orange on sour orange rootstock. This variegation is not infectious and should not be confused with that caused by infectious variegation-crinkly leaf virus (Phassouri orchard, Limassol, Cyprus)

FIGURE 315 Ortanique tangor on sour orange rootstock suddenly killed by the mal secco fungus, Deuterophoma tracheiphila (Petri), invading the tree from the soil through the roots. In mast cases infection is in the canopy and trees are not killed so suddenly (see Figures 232 to 235) (Lanitis orchard, Limassol, Cyprus)

FIGURE 316 Clementine tree on Poncirus trifoliata showing exocortis induced bark scaling on the rootstock (Boufarik Experiment Station, Boufarik, Algeria)

FIGURE 317 Rows of trees on Poncirus trifoliata rootstock. Trees in centre row are affected by exocortis; tree in Figure 316 is the first tree in the row. Trees in the row on right were also affected by exocortis. They were approach grafted to sour orange seedlings (see Figure 318) and have grown well ever since

FIGURE 318 Rootstock of the first tree In row on right in Figure 317. The central rootstock is me initial Poncirus trifoliata rootstock which is still showing exocortis bark scaling. The lateral rootstocks come from sour orange seedlings that were approach-grafled to the Clementine scion above the P. trifoliata stock. The exocortis-tolerant sour orange rootstocks have taken over and have allowed the trees to grow well

FIGURE 319 Normal Poncirus trifoliata tree on sour orange rootstock. This is a rare combination as P. trifoliata is usually seen as a seedling tree or as the rootstock of a grafted tree (Ferme Blanche, Oued Fodda, Orleanville region, Algeria)

FIGURE 320 Exocortis-affected tree on sour orange rootstock. Usually, exocortis-bark scaling is seen on Poncirus trifoliata used as a rootstock. Here, exocortis symptoms are seen on P. trifoliata used as a scion. Compare with exocortis-tree tree in Figure 319 (Ferme Blanche, Oued Fodda, Orleanville region, Algeria)

FIGURE 321 Poncirus trifoliata shoot from exocortis-affected tree in Figure 320, with yellow blotches typical of exocortis

FIGURE 322 View of Bouregreg River, with Salsola kali plants in the foreground and the city of Rabat, with "Hassan" tower, the landmark of Morocco, in the background. Hundreds of Neoaliturus haematoceps leafhoppers were captured on the S. kali plants. Several Spiroplasma citri-infected periwinkle plants were discovered in ornamental flowerbeds near "Hassan" tower in 1978 and 1990. The proximity of S. kali plants harbouring M haematoceps, the leafhopper vector of S. citri, probably explains why S. citri-infected periwinkle plants are found nearby. Notice that some S. kali plants are still green, others are brownish. In fact S. kali plants grow throughout the year and support continuous populations of M haematoceps

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