Inheritance and effects of the photoperiod sensitivity in foxtail millet (Setaria italica P. Beauv)

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Photoperiod-sensitive male sterility is a useful tool for exploitation of the heterosis in foxtail millet (Setaria italica P. Beauv), especially of the inter-specific cross using a two-line system. A foxtail millet photoperiod-sensitive male sterile line JG1S was identified in our hybrid breeding program which exhibited complete sterility under natural long daylight conditions (14.5 h d−1) and partial fertility under short daylight conditions (10 h d−1). The genetic basis of photoperiod-sensitive male sterility in JG1S was studied using nine F1×F2 and BCF1 progeny populations descended from crosses between JG1S as the female parent and nine fertile varieties as male parents. The F1 plants showed complete fertility similar to their male parents, indicating this photoperiod-sensitive male sterility was conferred by nuclear recessive gene(s). The testcross F2 and BCF1 that descended from three F1 fit a ratio of 1:3 and 1:1, respectively, while the testcross F2 and BCF1 descended from other six F1 fitted a ratio of 1:15 and 1:3, respectively. Therefore, it was inferred that two pairs of major recessive genes controlled the photoperiod-sensitive male sterility of JG1S. To establish which developmental stages are sensitive to photoperiod, and how the light integral affects plant fertility, two experiments were designed to evaluate the factors on photoperiod-sensitive male sterility by using reciprocal transfer experiments between long daylight (≥14 h d−1) and short daylight (10 h d−1) in specific developmental phases. The effects of photoperiod on the plant sterility and fertility were examined by using experiments in controlled chambers at seven photoperiod regimes (9 h d−1–15 h d−1). Plants were sensitive to photoperiod between the panicle initiation stage and the anthesis stage, with the greatest sensitivity observed in the phase from the panicle initiation stage to the floral primordial initiation stage. The plant fertility rate differed with the variation of photoperiod duration. The 13 h d−1 was a critical photoperiod regime for transformation between plant sterility and fertility. The plants remained completely sterile when photoperiod was 14 h d−1 or longer, and a higher fertility frequency was induced under photoperiod regime of 12 h d−1 or shorter.