Cytoplasm diversification was recognized as one of the most important objective in sustainable exploitation of heterosis. Isonuclear alloplasmic cytoplasmic male sterile (CMS) lines with Moricandia arvensis (mori), Diplotaxis erucoides (eru), Diplotaxis berthautii (ber) cytoplasms were developed in the six diverse Brassica juncea genetic backgrounds (NPJ 112, NPJ 139, LES 1-27, SEJ 8, EC 308575 and Pusa Agarni). Each of these 18 CMS lines were crossed with six locally developed restorers possessing fertility restorer gene from Moricandia arvensis to assess the effect of sterile cytoplasms and nuclear backgrounds of parental lines (A and R) on fertility restoration. Comparison of 108 single cross hybrids, 36 hybrids in each cytoplasm, revealed that the hybrids based on mori cytoplasm was significantly different from the ones possessing ber and eru cytoplasms for mean percent pollen fertility. Further, paired comparisons of the mean per cent pollen fertility of hybrids revealed that the per cent pollen fertility in hybrids was influenced by the genetic backgrounds of parents. However, this effect was not consistent for any cytoplasm or nuclear background of parents. Regression analyses involving percent pollen fertility and seed set in the hybrids, both under open and self pollinated conditions, did not observe any significant association. For diversification of mori based CMS-FR systems eru and ber cytoplasms can be used for sustainable exploitation of heterosis in Indian mustard.

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Predicting hybrid performance from the parental generation could largely enhance the efficiency of hybrid breeding programmes. To determine the relationship of parental distances estimated from phenotypic traits and SSR markers with F1 performance, average heterosis and heterobeltiosis in 44 indigenous and exotic genotypes of Indian mustard [Brassica juncea (L.) Czern. and Coss.], were studied. Jaccard’s genetic distances (JD) and Manhattan genetic distances (MD) were taken as criteria to classify the genotypic pairs into four diversity groups, viz. high, intermediate high, intermediate low and low. Seventy crosses representing the four diversity groups each for JD and MD were evaluated. Placement of higher number of significantly better hybrids was in extreme diversity groups created using JD, while, it was higher in intermediate diversity groups generated through MD. Low regression values were observed between JD among genotypic pairs and mean performance (R2 = 0.02), average heterosis (R2 = 0.046) and heterobeltiosis (R2 = 0.15). Similarly, low regression values were observed between MD among genotypic pairs and mean performance (R2 = 0.033), average heterosis (R2 = 0.046) and heterobeltiosis (R2 = 0.009). The slope of linear regression curve, placement of hybrids on the plot and low regression values in all the cases revealed that there is no significant association between genetic distance and hybrid performance. Therefore, desirable genetic diversity, in form of heterotic pools, needs to be identified from indigenous and exotic germplasm for expression of heterosis.

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