| How to overcome hybrid necrosis in wheat?
H.S. DHALIWAL, S.K. SHARMA and A.S. RANDHAWA Regional Research Station, Punjab Agricultural University Gurdaspur, Punjab, India Hybrid necrosis occurs in wheat due to the complementary gene interaction of dominant alleles of the two loci Ne1 and Ne2 (HERMSEN 1963). Of the two complementary necrotic genes, Ne1 is widely regarded as typical of durum wheat. Bread wheat cultivars with Ne1 gene are known to have derived their Ne1 from T. durum through artificial crosses between the non-carrier bread wheat (ne1 ne1 ne2 ne2) and Ne1 Ne1 ne2 ne2 durum wheats. Hybrid necrosis restricts the gene flow between T. durum and T. aestivum wheat varieties with Ne2 gene and even among T. aestivum varieties. In order to permit free gene flow amongst wheat and durum cultivars, it is very important to overcome the hybrid necrosis phenomenon. Certain necrotic F1 hybrid combinations were grown simultaneously in the off-season nursery in the summer, 1982 at Keylong (Himachal Pradesh) at a low temperature varying from 4 to 20C as well as at Gurdaspur in the green house at a higher temperature ranging from 30-38C. The F1 hybrid combinations sown at Keylong died of hybrid necrosis, while the ones at Gurdaspur survived. It was, therefore, surmised that the hybrid necrosis is expressed only at low temperature. Attempts were made to ascertain the threshold temperature below which the hybrid necrosis appears. Two necrotic hybrid combinations, one involving two T. aestivum cultivars viz. WL711 and C306 with Ne2 and Ne1 genes respectively (RANDHAWA, DHALIWAL & SHARMA, 1983) and the other involving T. aestivum cultivar WL711 with Ne2 gene and T. durum variety PBW34 with Ne1 gene, were grown in the field at weekly intervals throughout the growing season of wheat from November, 1983 to April, 1984. Under the field conditions neither of the necrotic hybrid combinations survived at any of the sowings. During this period highest minimum temperature of 24C was observed in April, 1984. This indicated that the lowest threshold temperature for hybrid necrosis could still be higher than 24C. Subsequently the F1 hybrid seed of the two necrotic crosses were grown at a constant temperature of 28C in the growth chamber from August to November, 1984. The hybrid necrosis did not appear at 28C in both the crosses. F2 seeds were obtained from the F1 hybrid WL711 x C306. The other cross WL711 x PBW34 failed to flower as it did not receive any of the required vernalization treatment. To circumvent hybrid necrosis in critical crosses in the breeding programmes the F1 hybrids should preferably be grown under controlled conditions at a temperature between 28-35C at which the hybrid necrosis does not appear and also a reasonable seed set is obtained. References HERMSEN, J.G. TH. 1963. The genetic basis of hybrid necrosis in wheat. Genetica 33 : 245-87. RANDHAWA, A.S., DHALIWAL, H.S. & SHARMA, S.K. 1983. Hybrid necrosis in wheat. Indian J. Genet. 43 : 370-373. |