Genetics of resistance to bacterial soft rot (Erwinia carotovara John), rootknot nematode (Meloidogyne incognita), yield and yield contributing characters in carrot (Daucus carota L.).

Abstract

Bacterial soft rot and root-knot nematodes cause great loss in yield and quality of the carrot root. The development of varieties resistant to bacterial soft rot and root-knot nematode is one of the ways to overcome these diseases. The present investigation was carried out i) to locate the source of resistance to bacterial soft rot and root-knot nematode ii) to locate the source of combined resistance to bacterial soft rot and rootknot nematodes and iii) to study the genetics of resistance to bacterial soft rot and rootknot nematode and yield contributing characters. Ten genotypes including 5 resistant and 5 susceptible lines each for soft rot and root-knot nematodes were selected by screening under natural epiphytotic and pot conditions. These lines were crossed in a diallel manner (excluding reciprocals). The data were collected for nine quantitative traits each for soft rot and root-knot nematodes. Ten lines exhibited resistance to soft rot viz., IHR 174-2, IHR-89, IHR 37-B-III, A+-PHG, IHR 64-89-HC-1, IHR 308 X PP-A, HYDC-4, IHR 309 and IHR 190 and ten genotypes for root-knot nematodes viz., HYDC-4, PKR, IHR 310, IHR 174-1, IHR 308, IHR 181, Danvers Half Long, Nantes, PYD-III AND Avenger and also combined resistance in two genotypes HYDC-4 and IHR 308. The heterosis over mid parental value indicated non-additive gene action for all the characters. Combining ability analysis revealed higher gca to sca variance for all the characters except for percent disease index suggesting predominance of additive genetic variance for these characters. Dominant gene action was more involved than additive gene action for all the characters except PDI and PGI for which additive gene action was found to be operating. The hybrids IHR174-2 x Desi Red, IHR 37-B-III x Sersa local, PPA x Sersa local, PP-A x IHR 21, IHR 64 x LL-2 and the crosses IHR 174-1 x IHR 301, IHR 301 x IHR 174-2, IHR 301 x IHR 300 and IHR301 x IHR 181-2 could be used in recurrent selection for sca and heterosis over mid parent to bring about desirable improvement in terms of high root weight, and resistance to bacterial soft rot and root-knot nematode, respectively.