Determining the Efficacy of a Hybridizing Agent in Wheat (Triticum aestivum L.)

Abstract

Hybrid wheat (Triticum spp.) has the potential to boost yields and enhance production under changing climates to feed the growing global population. Production of hybrid wheat seed relies on male sterility, the blocking of pollen production, to prevent self-pollination. One method of preventing self-pollination in the female plants is to apply a chemical hybridizing agent (CHA). However, some combinations of CHA and genotypes have lower levels of sterility, resulting in decreased hybrid purity. Differences in CHA efficacy are a challenge in producing hybrid wheat lines for commercial and experimental use. Our primary research questions were to estimate the levels of sterility for wheat genotypes treated with a CHA and determine the best way to analyze differences. We applied the CHA sintofen (1-(4-chlorphyl)-1,4-dihydro-5-(2-methoxyethoxy)-4-oxocinnoline-3-carboxylic acid; Croisor 100) to 27 genotypes in replicate. After spraying, we counted seed in bagged female heads to evaluate CHA efficacy and CHA-by-genotype interaction. Using logit and probit models with a threshold of 7 seeds, we found differences among genotypes in 2015. Sterility was higher in 2016 and fewer genotypic differences were found. When CHA-induced sterilization is less uniform as in 2015, zero-inflated and hurdle count models were superior to standard mixed models. These models calculate mean seed number and fit data with limit-bounded scales collected by agronomists and plant breeders to compare genotypic differences. These analyses can assist in selecting parents and identifying where additional optimization of CHA application needs to occur. There is little work in the literature examining the relationship between CHAs and genotypes, making this work fundamental to the future of hybrid wheat breeding.

Assessing the Suitability of Elite Lines for Hybrid Seed Production and as Testers in Wide Crosses With Wheat Genetic Resources

“…variance of sterility of the female line (Table 2). This can be explained by a strong influence of weather conditions such as rain, wind or heat on the efficiency of the chemical hybridization agent as noted in previous studies (Pickett, 1993;Kempe and Gils, 2011;Whitford et al, 2013;Easterly et al, 2019). Moreover, the genotype also significantly (P < 0.001) contributed to the phenotypic variance of sterility, resulting in a broad-sense heritability of h 2 = 0.32, which is surprising, since Clofencet, the applied chemical hybridization agent, is expected to act relatively independent of the wheat genotype (Parodi and de los Angeles Gaju, 2009;Nesvadba et al, 2001;Kempe and Gils, 2011;Whitford et al, 2013).…”

Heterosis in crop improvement

“…The first commercially available wheat hybrids were achieved through chemical emasculation, that is, chemical castration of designated females. However, the emasculation rate was suboptimal resulting in seeds with unsatisfactory purity (Basnet et al., 2022), and too expensive to reach high purity (Easterly et al., 2019). This led to the transition toward more robust cytoplasmic and genetic male sterility systems (Adugna et al., 2004; Bohra et al., 2016; Gupta et al., 2019; Longin et al., 2012).…”

Prospects for Trifolium Improvement Through Germplasm Characterisation and Pre-breeding in New Zealand and Beyond

“…The possibility of using new chemical agents for the induction of male sterility could play a major role in hybrid clover seed production in the future (Easterly et al, 2019). Sterile male plants increase the feasibility of producing hybrids of cross-pollinated species that traditionally utilise a population improvement method.…”