Calcium May Help Decrease Rice Straighthead in a Silt Loam Soil.

Straighthead is a physiological disease in rice which causes blanking of the panicle and can result in complete yield loss. Using the US cultivar Cocodrie and three breeding lines, 8-18, 8-9 and 12-38, we tested the effect of Calcium (Ca) application on the development of straighthead symptoms in the greenhouse. Three plants were grown in each pot (22 cm tall and 22 cm diameter) using silt loam soil from a site known to have naturally occurring straighthead with three replications. Four Ca treatments were applied to each pot for the three lines and straighthead susceptible check Cocodrie. This included 297g Ca (Calcium carbonate) applied at the vegetative stage (V-Ca), 535g Ca at booting stage (B-Ca), and V-Ca plus B-Ca (VB-Ca). During the season, variation in straighthead symptoms, including sterile and deformed grains and panicles, were observed due to Ca treatments and genotypes. At maturity, 5 representative panicles were harvested from each pot to score seed set (%) for measuring straighthead.  ANOVA analysis based on the seed set showed highly significant variation (p<0.0001) due to genotype, Ca, and their interaction.  Cocodrie was most susceptible with an average seed set of 19.02%, while line 8-9 was most resistant with a seed set of 80.30%. The pair-wise differences in seed set among all 4 genotypes were significant. VB-Ca resulted in the highest seed set of 70.45% which was significantly higher than V-Ca of 47.59% and B-Ca of 45.58%. The check with no Ca treatments had the lowest seed set of 31.12% which was significantly lower than any one of Ca treatments. For susceptible Cocodrie and 8-18 had almost no seed set (1.00 and 8.90%) in the untreated soil, while VB-Ca recovered Cocodrie to 52.16% and 8-18 to 61.76% seed set. For resistant 8-9 and 12-38 had 63.50 and 68.97% seed set on the untreated soil, respectively, while VB-Ca increased their seed set up to 89.96 and 74.28%, respectively.  Our results suggest that Ca may help reduce straighthead symptoms and recover seed set of rice.