COLD-RESISTANT LUCERNE (Medicago sativa)
FOR NORTHERN XINJIANG, CHINA*
Xinjiang Uygur Autonomous Region is in the extreme north-west of China; its climate is arid to semi arid and markedly continental with very cold winters; much of the region is mountainous. Extensive livestock rearing, mainly by traditional, transhumance is therefore a major land use. Crop production is mostly limited to the traditional oases and some modern irrigation developments which have been installed in the past half century. The herdsmen belong to minority nationalities, Kazakh, Kyrgyz and Mongol. Good grazing is only available, on mountain pastures, in summer; production and fattening is, therefore, based on the summer pastures. The winter is very long and the herds have to survive on very meagre grazing at lower altitudes by the desert fringe; winter and spring losses are often heavy. Provision of winter feed to improve survival and delay the move to spring pastures (which are regularly damaged by being grazed too early) is an important tool in attaining better herd output, higher family income and in reducing damage to the transition pastures.
Lucerne, Medicago sativa L., is a crop of very ancient cultivation in the irrigated areas of Xinjiang and is the main crop grown for hay for winter feed. Large areas of lucerne are being developed in the north of Xinjiang, an arid region with very cold winters. Given the very limited number of cultivars it was deemed desirable to have a wider genetic base. Under a UNDP/FAO project a large number of cold-tolerant, disease-resistant lucernes, mostly from North America, were identified and introduced for screening. Their testing was undertaken by the Xinjiang Agricultural University at Altai. The initial growth of many of the introductions was impressive and their first year performance far outstripped the local control (Beijang). Next spring, however, none of the introductions survived at Altai (except for a few isolated plants) - only the control was alive! The project sites, on the desert fringe, have little or no snow cover in winter so the young plants had no protection; perhaps they had been selected in areas with snow cover. It later transpired that earlier introductions from Russia had failed in a similar way. There was, therefore, no easy way to diversify and improve the lucernes in use by importation of commercially available cultivars. After discussions with the fodder specialists of Xinjiang Agricultural University the Grassland and Pasture Crops Group of FAO/AGPC agreed to provide some support so that the Universitys ongoing work on local breeding and selection of lucerne could be intensified.
DEVELOPMENT OF XINMU NO. 3 LUCERNE
In 1995 thirty three plants were selected, when they greened up in spring, from a four-year-old plot of Spredor2** lucerne at Urumqi; the Spredor2 had been sown in 1990 and grown unprotected through the subsequent winters; the selection was made among the survivors. These were open pollinated and the seeds mixed to form line 9501 (later relabelled Xinmu No 3). Some stems were taken as cuttings and taken to 183 Farm, Beitun, Altai (hereafter referred to as Altai) in August for cold tests. Splits of twelve mother plants were grown in a greenhouse to speed up seed production; seed was harvested in November.
Four cultivars were chosen for testing at Altai and Urumqi from 1996; line 9501, Beijang, Xinmu No. 1 and Spredor2. These were sown in randomised block with three replications at both sites in plots of 5.63 m2 with a 30 cm row spacing and a seed rate of 3 kg/ha. Harvest was at early flowering (2 - 3%) with two-and-a-half cuts at Urumqi and two at Altai. The last cut was taken one month before growth was expected to stop. Five hundred gramme samples were air-dried for dry-matter estimation. The trials received five to six weedings, three to four hoeings and five to six irrigations annually. Yield data are given in Tables 1 and 2.
Line 9501 was the highest yielder throughout the trials at both sites. In both cases second year yields were much higher than those of the seedling or third year - this may be due to the absence of maintenance fertiliser - normal practice on the Altai scheme.
Table 2 Yield trial at Altai over three years; tonnes per hectare air-dry material
Testing for cold resistance was done at both sites. Surviving and dead plants were counted after greening up each year; since some plants which were injured by low temperatures, but had not died, greened up 3 to 20 days later than normal plants three counts were made. Plants which had not greened up at the first counting were marked; if they greened up at the second or third counting the were added to the survivors; those which had not greened up by the branching stage were counted as dead. Results for the two sites are given in Table 3. Survival was very good throughout; all entries in the trial were, of course, known to be adapted to local conditions. Survival of Spredor2 and Beijang at Urumqi in the third year was much poorer than that of line 9501 and Xinmu No. 1 but at Altai all survival rates were similar.
The effect of removal (by brushing) of any snow cover from the third replicate was studied between November and April of the establishment year (Table 4). Snow removal delayed greening up by a few days and caused a small decrease in survival.
As part of the characterisation of the new cultivar for registration, phenological data and information on the proximate composition of its forage were collected. 9501 (renamed Xinmu No 3) has at least as good a feeding value as Beijang.
Overwinter survival, of course, reflects more than cold tolerance, disease susceptibility is also involved. In all both line 9501 (Xinmu No 3) was superior. Snow removal led to a mortality of between three and six percent with no difference between line 9501 (Xinmu No 3) and Beijang.
As formal testing advanced, field-scale observations were installed at Beitun/Altai and Urumqi, under conditions similar to those used by herders to see how the selection performed as a commercial cultivar. As can be seen from Table 5, line 9501 performed well at both sites.
Seed production of line 9501 was a priority from the outset to provide enough for proper testing; now that the line has shown promise provision of breeders and foundation seeds is being organised so that these can be supplied to producers. It is necessary that a well supervised three-step production system (breeders seed à foundation seed à certified seeds) be used for future lucerne seed production. Clean, dodder-free, healthy seed of adapted varieties is the key to sustainable, high yielding lucerne production in Altai.
The very cold, arid areas of northern Xinjiang pose a problem when broadening the genetic base of lucerne cultivation, especially since introduction of cultivars from elsewhere does not succeed. Earlier work (development of Xinmu No 1 and Xinmu No 2) showed that considerable progress can be made by working with local material. The work described above shows that introduced material can have a very positive role in lucerne improvement, at least insofar as material with some M. falcata in its background is concerned. The cultivar Xinmu No 3 has shown itself to be superior in yield to the cultivars currently in use and well adapted to the conditions and methods of husbandry used locally. It may well prove to be valuable through a much wider area in the colder arid tracts of Northern China and North-eastern and Central Asia.
* Unpublished data taken from a forthcoming paper by Min Jichun et al.
** Spredor2 was released by Northrup King in 1974, its parentage is Travois, Rambler and Vernal; these are cold tolerant cultivars with Ladak, M. falcata, Siberian, Cossack among their parents. Spredor2 has variable flower colour; it is highly resistant to bacterial wilt and moderately resistant to verticillium wilt and fusarium wilt.