DH sterile line selection and its stability evaluation in sterility

The sterility of DH lines obtained during 2015–2017 was independently evaluated by sowing at two dates on Oct.15 and Nov. 20, respectively (Fig. ​(Fig.3).3). At least 10 spikes per line in each sowing were randomly bagged before flowering to measure the seed setting rate. The out-crossing potential (glume opening, stigma exsertion) [17], and other important traits such as disease resistances and yield potential were also recorded. Lines with sterility higher than 95% in both sowings were kept for stability evaluation of sterility next year.

Selected lines in 2015/2016 and 2016/2017 growing seasons were repeatedly evaluated in 2016/2017 and 2017/2018 seasons. For F₁-derived elite DH lines, we also conducted a ten-sowing assessment in the third year from Oct. 22, 2017 to Dec. 24, 2017 with an interval of 7 days. The TPSGMS line K78S was used as the check in all tests. The seed setting rate (SSR) was calculated following Yang et al. (2006) [16]:

Where gn means the number of grains from bagged spikes, sn the number of spikelets. A TPSGMS line with SSR < 5% was recognized as highly sterile and qualified for hybrid seed production [16].

Temperatures during 2016–2018 were collected from a data-logger ‘HUATO S100-TH’ in thermometer screen near the field, and daylengths from the meteorological station of Kunming.