Heterotic groups of tropical indica rice germplasm

Abstract

Four heterotic groups were identified for tropical indica rice germplasm to develop hybrid rice in the tropics based on two studies. Heterotic groups are of fundamental importance in hybrid crop breeding. This study investigated hybrid yield, yield heterosis and combining ability within and among groups based on genetic distance derived from single-nucleotide polymorphism markers. The main objectives of the study were to (1) evaluate the magnitude of yield heterosis among marker-based groups, (2) identify possible heterotic groups for tropical indica hybrid rice, and (3) validate heterotic patterns concluded from a previous study. Seventeen rice parents selected from improved indica germplasm from the tropics with high genetic divergence and 136 derived hybrids were evaluated in five environments. The hybrids had more yield than their parents with an average of 24.1 % mid-parent heterosis. Genotype × environment interaction was the major factor affecting variations in yield and yield heterosis, which raised a necessity and a challenge to develop heterotic rice hybrid adapted to different regions and seasons in the tropics. Yield, yield heterosis and combining ability were significantly increased in inter-group than in intra-group hybrids. Four heterotic groups and three promising hybridization patterns, which could be used in tropical hybrid rice breeding, were identified based on marker-based grouping, yield and yield heterosis analyses in the two studies. The study reveals that molecular markers analysis can serve as a basis for assigning germplasm into heterotic groups and to provide guidelines for parental selection in hybrid rice breeding.

Genome-Based Identification of Heterotic Patterns in Rice

“…1). The slightly higher values compared to the previously reported ones (Cheng et al 2007a; Huang et al 2016; Wang et al 2014; Xie et al 2013) can be explained by the moderate phenotyping intensity and the augmented design used in our study with unreplicated evaluation of hybrids but replicated evaluation of line varieties. The different allocation of resources for checks and hybrids was caused by restrictions in hybrid seed production.…”

“…The yield advantage of rice hybrids over released line varieties, which is often denoted as commercial heterosis, was reported to be in the range of 10 to 20% (Cheng et al 2007a; Huang et al 2016; Wang et al 2014; Xie et al 2013). We estimated the magnitude of the commercial heterosis by contrasting grain yield of the phenotyped hybrids with the performance of the highest-yielding line variety included in the trials.…”

“…Several approaches have been used to reduce the sterility occurring when crossing indica and japonica (Guo et al 2016; Ouyang et al 2010), but none of them has been successfully implemented into hybrid rice breeding programs. The search for heterotic groups within the major germplasm pools is limited to studies based on tropical indica rice (Wang et al 2014; Xie et al 2013). Moreover, previous studies used molecular marker-based genetic distances as proxy of the heterosis or hybrid performance, which is unreliable for unrelated parental inbred lines (Melchinger 1999; Xu et al 2014; Xu et al 2016).…”

Breeding Self-Fertilizing Plants: From Inbred to Hybrid Cultivars

“…Genes for such traits and fertility restoration are available and being bred into elite germplasm by MAB (Xu 2003). Four heterotic groups and three promising hybridization patterns, which could be used in tropical hybrid rice breeding, were noted with the aid of marker-based grouping, yield and yield heterosis analyses (Wang et al 2014b). DNA marker-aided reciprocal recurrent selection also facilitates the pyramiding of heterosis genes from various rice ecotypes.…”

A unified framework for hybrid breeding and the establishment of heterotic groups in wheat

“…In contrast to maize, the absence of a clear association between genetic distance and heterosis might also be explained by the generally low level of heterosis in wheat. For example, for the development of heterotic groups, in addition to grouping of diverse germplasm based on molecular markers, testcrosses for the identification of good combiners are still necessary (Melchinger and Gumber 1998) as demonstrated in maize (Menkir et al 2004) or in rice (Wang et al 2015). Furthermore, the findings from Zhao et al (2016) indicated that genetic distance, while not sufficient, is nevertheless required for high hybrid performance, thus underscoring the need for a more unified approach.…”