ICARDA Annual Report 1998

Interspecific Hybridization in Chickpea

The cultivated chickpea (Cicer arietinum L.) belongs to the genus Cicer, which comprises an additional eight wild annual species. The wild Cicer species, in general, possess higher levels of tolerance to many key biotic (ascochyta blight, fusarium wilt, nematodes, bruchids, leaf miner, pod borer) and abiotic (cold, heat, drought) stresses than the cultivated species. At ICARDA, researchers have successfully crossed the domesticated with the two most-closely-related wild Cicer species: C. reticulatum and C. echinospermum. This has allowed the transfer of high levels of cold and cyst nematode tolerance from these wild species to the cultigen. The other wild Cicer species of interest are C. bijugum, C. pinnatifidum and C. judaicum, which possess high levels of tolerance to various biotic and abiotic stresses (ascochyta blight, bruchids, leaf miner, nematodes, drought, and cold). Earlier attempts at ICARDA to produce viable interspecific hybrids involving these wild species (C. bijugum, C. pinnatifidum, C. judaicum) and kabuli chickpea were not successful. During the 1997/98 season, desi chickpea was included in hybridization with the wild types. The interspecific crosses using these wild species generally resulted in very low seed set. Seed set was more among the crosses between the cultigen and C. judaicum than the crosses between the cultigen and either C. pinnatifidum or C. bijugum. Further joint research with Italian institutions on crossability barriers between the cultigen and C. judaicum and C. pinnatifidum showed the absence of any pre-zygotic barrier to the incompatibility in hybridization. To overcome the post-zygotic incompatibility barriers, different hormones were used at various stages of plant growth. An application of a hormone solution [gibberelic acid (8 mg/l) + kinetin (5 mg/l) + naphthalene acetic acid (25 mg/l)] after pollination led to ovules from which embryos could be rescued. The seeds from these interspecific crosses are now being tested for their fertility and multiplication.

Survey of Lentil and Chickpea Viruses in Ethiopia

Upon the request of the Ethiopian Agriculture Research Organization (EARO), scientists from ICARDA, Ethiopia, Egypt, and Yemen conducted a survey of virus diseases affecting chickpea and lentil in Shewa province of Ethiopia in November 1998. The survey covered 33 randomly selected chickpea and 32 lentil fields. Virus disease incidence was determined based on laboratory examination of 100-200 randomly collected samples from each field against antisera of 12 viruses. Over 9000 chickpea and lentil samples were tested, using the tissue-blot immunoassay procedure at Debre Zeit Research Center. In chickpea fields, beet western yellows virus (BWYV) and soybean dwarf virus (SbDV) were the most common. Five chickpea fields had a virus disease incidence of 21% or higher (Fig. 10). In lentil fields, pea seed-borne mosaic potyvirus (PSbMV) was the most common, followed by BWYV and SbDV. Eleven lentil fields (34% of the fields surveyed) had a virus disease incidence of 21% or higher. The highest virus disease incidence in a single field was 58.5% in lentil (PSbMV) and 41.3% in chickpea

(BWYV). Other viruses, though rare, found during the survey included the faba bean necrotic yellows nanovirus (FBNYV) and broad bean wilt fabavirus (BBWV) in chickpea; and FBNYV, broad bean stain comovirus (BBSV), bean yellow mosaic potyvirus (BYMV), and cucumber mosaic cucumovirus (CMV) in lentil.

Management of Lentil Vascular Wilt

Lentil vascular wilt, caused by Fusarium oxysporum f.sp. lentis, is a widespread and devastating disease in most countries where lentil is grown. It sometimes causes complete crop failure, especially in a warm and dry spring.
         ICARDA annually screens, under well-established "sick-plot" conditions, germplasm and breeding lines for sources of resistance to wilt. The wilt-resistant material is then distributed to national programs. As a result, 'Talya 2' is being grown by farmers in Lebanon; a wilt-resistant line ILL 5883 is a candidate for release in Syria; and NARS scientists in Ethiopia, Sudan, and Egypt have also identified resistant sources from ICARDA-supplied material.
           To increase the durability and reliability of the management of the disease, host-plant resistance was integrated with other components including soil solarization, adjustment of planting date, and chemical seed treatment. Results showed that early planting in November gave a higher economic yield than late planting in December and January in wilt-infested soil. Even with moderately resistant genotypes, early planting combined with soil solarization provided 74% more seed yield than unsolarized late sowing. Soil solarization is also a means to control weeds, which are more severe in early sowing. Seed treatment with the fungicide benomyl (Benlate) showed no effect on reducing wilt infestation and may not be useful in the integrated management of the disease.
           Clearly, integrated management of lentil vascular wilt is agronomically possible. It allows lentil cropping in fields previously abandoned for lentil due to soil wilt infestation either by using resistant varieties in early sowing or moderately resistant ones with soil solarization. However, the economics of soil solarization needs further investigation before formulating recommendations for farmers.

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