Hybrid breeding in many self- pollinated crops is less successful because of the lower magnitude of heterosis. Several factors such as high seed densities coupled with difficulties to implement a cost-effective system for hybrid seed production, lower selection gain for hybrid compared to line breeding are attributed to less success of hybrid breeding in self-pollinated crops. Heterosis in self-pollinated crops is often driven by additive and additive x additive gene action. Compared to non-additive heterosis, additive form of heterosis can be fixed in homozygous lines quickly and their seed can be easily resown to carry the same “heterosis” over generations. Therefore, a new integrated breeding strategy called Hybrid enabled-line profiling (HELP) was proposed that enables identifying a high frequency of superior lines that is fixed with heterosis due to additive gene action in self-pollinated crops.

This strategy enables the performance of F1 hybrids to guide the profiling and development of F1 derived lines or doubled haploids (DHs). Based on F1 hybrid testing, only the very top hybrids are promoted for line or DH derivation which further dramatically reduces the number of crosses being promoted while increasing the likelihood of obtaining superior new cultivars. In Hybrid enabled-line profiling, the F1 hybrids themselves are not the end product of commercial cultivars, rather hybrids help to identify near homozygous lines or DHs which are then released as varieties.

Prediction of heterosis in hybrid rice based on genomic, transcriptomic and metabolomic data using six different prediction methods (LASSO, BLUP, SSVS, PLS, SVM-RBF and SVP-POLY). They found that among six prediction methods, LASSO and BLUP are the most efficient methods for yield prediction.

There is ample scope to exploit heterosis in selfing crops by integrating genomic, biotechnological and bioinformatic tools. HELP is such a new integrated breeding strategy which focuses on the most superior crosses. This focus results in significant increases in efficiency and can reverse the edible yield plateauing feared in some of our major selfing food crops.

References:

GINKEL, M. V. AND ORTIZ, R., 2018, Cross the best with the best, and select the best: HELP in breeding selfing crops. Crop Sci., 58:17-30.

XU, S., XU, Y., GONG, L. AND ZHANG, Q., 2016, Metabolomic prediction of yield in hybrid rice. The Plant J., 88(2):219-227.