Abstract
The sensitivity of sorghum to pre-flowering cold stress, resulting in reduced pollen viability and poor seed set, is a major constraint for expanding growing areas into higher altitudes and latitudes. Nevertheless, compared to juvenile cold tolerance, reproductive cold tolerance in sorghum has received much less attention so far, and very little is known about its inheritance in F1-hybrids. We have composed a representative factorial (n = 49 experimental F1-hybrids) for a comprehensive study on heterosis and combining ability for crucial tolerance traits as spikelet fertility (panicle harvest index), seed yield and pollen viability, using field trials in stress- and control environments in Germany and Mexico as well as climate chamber experiments. Our results indicate a heterotic and rather dominant inheritance of reproductive cold tolerance in sorghum, with strong effects of female general combining ability (GCA) on F1-hybrid performance in our material. These findings, together with the comparatively low contribution of specific combining ability (SCA) effects and high heritability estimates, suggest that robust and efficient enhancement of reproductive cold tolerance is feasible via hybrid breeding.
Highlights
The sensitivity of sorghum (Sorghum bicolor(L.) Moench) as an originally tropical C4 -plant to temperatures below 15 ◦ C substantially obstructs its successful implementation into both high-latitude temperate climates and tropical high-altitude areas [1]
They were selected for this study due to (i) their different levels of reproductive cold tolerance shown in former experiments, aiming at a diverse, representative selection; (ii) their similar maturity, to minimize the influence of different weather conditions at critical growth stages distorting the results; (iii) their similar panicle architecture, being all of the Sorghum bicolor(L.) Moench subspecies caudatum and kafir or their intermediate types with semi-compact panicles, which can possibly reduce the impact of different panicle compactnesson Panicle Harvest Index (PHI) values under control conditions (for this reason, no material with extremely open or compact panicles, like Sorghum bicolor(L.) Moench subspeciesguinea or durra, was utilized)
Males as a group performed significantly better than females (Table 3, Figure 2)
Summary
The sensitivity of sorghum (Sorghum bicolor(L.) Moench) as an originally tropical C4 -plant to temperatures below 15 ◦ C substantially obstructs its successful implementation into both high-latitude temperate climates and tropical high-altitude areas [1]. While farmers can opt for later sowings to avoid juvenile cold stress (even though on the expense of the available growth period and yield potential), there is no escape strategy for cold spells during reproductive stage, which can induce male sterility leading to reduced or even no seed set and grain yield. Singh [1] measuredreproductive chilling tolerance in a set of 380 accessions, and identified tolerance sources originating mainly from Ethiopia, Uganda, the USA and China. This was the first study giving some information on the inheritance of this trait using factorial F1 hybrids. Several Mexican studies [9,10,11,12,13] deal with
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