- Frost and growth stage phenotype
Given the importance of establishing the plant growth stage during the
frost events, anthesis date and plant growth stages during ear emergence
were recorded for all populations in Williams and Muresk during the 2018
trials. In the Narrabri trials, the Zadoks stages around 50-60 were
recorded. Days to anthesis data were also recorded in the glasshouse, in
Wongan Hills and Katanning, in 2017. In 2018, days to maturity were
estimated for each plot at the Williams site as follows: on 31 October,
based on the plant maturity performance, the plant maturity scoring was
entered as 0 (mature) to 15 (based on an estimate of 15 days to
maturity).
In 2018, probably because of high rainfall and low soil temperatures in
August, the average anthesis time was delayed by 15 to 20 days in the WA
field trials. Flowering time ranged from 25 September to 12 October in
Williams, and from 13 September to 6 October in Muresk. The lowest
temperatures (-1.1 and 0.3oC, respectively) were
recorded on 14, 15 and 16 September in Williams, and 15 and 16 September
in Muresk (Fig. 1). Those temperatures lasted 300 and 130 mins in
Williams and Muresk, respectively. The low temperatures during heading
and anthesis caused frost damage in all six DH populations. The highest
frost damage was to spikes (Fig. 1). Ten heads were picked from each
plot for frost assessment around 20 days after anthesis. Three parental
lines (Bethlehem, Mace, and Westonia) and two control lines
(Wyalkatchem, Yitpi) from three anthesis windows were used, and 7 to 14
plots for each line were randomly selected for floret sterility
assessment (Supplementary Fig. 1a). Frost damage was scored visually by
a single person using a 0-15 scale
(0:
no frost damage; 1-2: a proportion of 0.5-5% of spikes damaged by frost
within a plot (95-99% of grain remaining); 3-4: 5-20% damaged (80-95%
of grain remaining); 5-6: 20-40% damaged (60-80% of grain remaining);
7-8: 40-60% damaged (40-60% of grain remaining); 9-10: 60-80% damaged
(20-40% of grain remaining); 11-12: 80-90% damaged (10-20% of grain
remaining); 13-15: 90-100% damaged (0-10% of grain remaining)
(Supplementary Table 5). The correlation coefficient between visual
frost damage and floret sterility was 0.79 (P <0.01)
(Supplementary Fig. 1b).