Sorghum (Sorghum bicolor (L.) Moench) is a major world crop that is a reliable source of fodder and food grain in arid regions. However, unlike other cereals, sorghum grain has low nutritional value, owing mainly to the resistance of its storage proteins (kafirins) to protease digestion. Changing the composition of kafirins or their primary structure may address this problem. To induce mutations in kafirin-encoding genes that were expected to disturb their accumulation in endosperm cells, we used a genome-editing approach. By Agrobacterium-mediated genetic transformation of immature embryos of cv. Avans, we obtained 14 transgenic plants with genetic constructs for site-directed mutagenesis of the k1C5 and gKAF1 genes encoding 22 kDa α- and 28 kDa γ-kafirins, respectively. Sequencing of 5 regenerants obtained by using k1C5-addressing vector revealed two plants with mutations. T₁ progeny of these mutants had higher in vitro digestibility of endosperm proteins (86%–92%), in comparison with the donor Avans (63%–67%). The kernels of these plants had a thick vitreous endosperm. A mutant with increased in vitro protein digestibility and vitreous endosperm, carrying a mutation in the target sequence, was also obtained by use of the gKAF1-addressing vector. Thus, using genome editing technology, we have obtained mutants with improved kafirin digestibility that can be used in sorghum breeding.

Use of cytoplasmic male sterility (CMS) in hybrid breeding requires effective male fertility-restoring lines. In sorghum, very few restoring lines that can restore fertility in A₃ CMS have been reported. To identify the reasons for this deficiency, F₁ and F₂ hybrids of an A₃ CMS line crossed with the line IS1112C, a donor of fertility-restoring (Rf) genes for A₃ cytoplasm, and testcrosses of fertile plants to A₃ CMS lines were grown under contrasting water availability regimes in dryland and irrigated field plots. In the irrigated plots the frequency of fertile plants in testcrosses was twice that in dryland plots (P<0.05). Fertile plants from the F₂ family grown in the irrigated plots showed significantly higher restoration ability than fertile plants from the same family grown in dryland plots. F₃ plants from the F₂ family grown in irrigated plots yielded on average a sixfold higher frequency of fertile plants in testcrosses than F₃ plants derived from dryland plots (P<0.01). Fertility of testcross hybrids correlated negatively with air vapor pressure deficit (VPD) at flowering (r=−0.96; P<0.01) suggesting that VPD is a trigger for downregulation of Rf genes for A₃ cytoplasm.