| Effect of gamma rays on the expression of hybrid necrosis
in wheat P. N. NARULA and O. P. SRIVASTAVA Regional Research Station, L.A.R.I., Pusa, Bihar, India Hybrid necrosis: a phenomenon characterized by the gradual perishing of F1 hybrid plants at one stage or the other, imposes serious limitation on the realization of desired recombinants in many cross-combinations involving indigenous wheat varieties, such as, N. P. 830, N. P. 839, N. P. 875, N. P. 883, C. 306 on one hand and Mexican dwarfs like Kalyan Sona, Chotti Lerma, Safed Lerma, Sonalika and many other European varieties, on the other. Hybrid necrosis which is based on two dominant complementary genes Ne1 and Ne2 (HERMSEN 1963, ANAND, GILL and JAIN 1969, NARULA, SRIVASTAVA and SRIVASTAVA 1970) each of which has multiple alleles controlling the degree of necrosis, is of wide spread occurrence (HERMSEN 1963, ZEVEN 1966, KIHARA and TSUNEWAKI 1962). It has been observed that indigenous varieties carry Ne1 while there is a preponderance of Ne2 in the Mexican dwarf varieties (NARULA, SRIVASTAVA and SRIVASTAVA 1970). Mexican dwarf varieties, which have been widely acclaimed for their explosive yield potential, do not command consumer's popularity in India as these do not only lack the chapati-making qualities but also the grain lustre characteristic of the Indian varieties. It has, therefore, been felt necessary to transfer the grain quality from the indigenous varieties to the well-adapted Mexican introductions. Because of wide spread occurrence of the Nes2 in the dwarfvarieties and Nes1 in some of the best Indian wheats, hybrid necrosis has imposed a ceiling on the choice of parental combinations. This also up-sets the programme of diallel cross-combinations. HERMSEN (1963) suggested methods to preclude hybrid necrosis by using non-carrier varieties; exploiting varietal impurity; introducing non-carrier as a bridging host and irradiating parental varieties to obtain non-carrier mutants. But as these methods are either time-consuming or limit choice of parents, it was desired to see if radiations could be used to inactivate the necrotic genes present in the F1 hybrids and foster recombinants in crosses which otherwise manifest severe necrosis at the seedling stage. Ten F1 seeds from the cross C. 306 (amber grained) x PV- 18 (red grained) were subjected to 16 kr. gamma rays at the Division of Genetics, I.A.R.I., New Delhi and the treated seeds were grown in pots at Pusa five days after the treatment was given. Five untreated crossed seeds were sown separately as control. Plants from treated seeds were harvested and threshed separately. M2 generation was space-planted in the field in the next rabi season and screened for hybrid necrosis. |
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