Rice hybrids may be a lot like the old Timex watches. They can take a licking from diseases such as sheath blight and keep on ticking, producing higher yields than conventional varieties in the process.
Robert Miller, plant pathologist with RiceTec Inc., says he noticed that one of the rice hybrids he was working with three years ago showed high incidence of disease when it was inoculated with sheath blight in paired plot studies.
But the yield losses were significantly lower in the hybrid — XL723 — at harvest than in conventional varieties with similar disease ratings in the studies conducted at the LSU AgCenter’s Rice Research Station.
Speaking at the recent RiceTec Field Day at its Arkansas Business Center near Harrisburg, Miller said rice hybrids typically have better disease ratings to most of the common diseases found in the southern Rice Belt states of Arkansas, Louisiana, Texas and Mississippi.
“Most of the resistance genes to the diseases are dominant in these hybrids,” he said. “So, if we have a gene in one parent that’s different than the gene in the other parent, when we cross them both genes are active in the hybrid. That tends to give us a much better disease package, and it will help minimize your risk.”
When it comes to sheath blight, the No. 1 disease in north Arkansas and in Louisiana and Texas, RiceTec’s hybrids are rated the same as Francis and Wells, two conventional varieties released by the University of Arkansas.
“When you go out in the field and you hand inoculate with sheath blight inoculum and compare the ratings, you’ll find that, yes, they do have a similar amount of disease — they’re rated MS or moderately susceptible,” said Miller.
“But we were doing similar work at LSU on some varieties where I had some paired plot work. I had one plot inoculated and the plot next to it was not inoculated. And I replicated that and looked at it across years, and came up with some interesting data.”
Miller found that even when hybrids and varieties have the same amount of disease, they experience different levels of yield loss. In LSU inoculated vs. non-inoculated studies, for example, Cocodrie generally loses about 15 percent of normal yield due to sheath blight.
“In the work I did over the last three years, I’ve seen up to a 20 percent yield loss,” said Miller. “You’ll note that Wells, which is moderately susceptible, was at 10 percent, XL8 was at 9 percent. But the surprise was XL723. It has the same amount of disease as Wells and XL8, but the yield loss was 2 percent.”
Miller said other plant pathologists have told him they’re seeing similar results for hybrid rice. “Rick Cartwright, Arkansas Extension plant pathologist, has said that in only one of 10 times did it pay to spray the hybrids with a fungicide,” he said. “You find out they don’t always have the yield loss you would expect from that amount of disease.”
Miller said he isn’t sure how much growers might be able to save on fungicide costs with hybrid rice. “That’s one of the things we’re looking at as we continue to study these hybrids.”
RiceTec leaders said they are evaluating two other rice hybrids with higher yields and strong disease-resistance packages for possible release in 2008.
“XL744 and Clearfield XL745 are both in their fourth year of evaluation,” said RiceTec President John Nelsen, who is based in Alvin, Texas. “If the data supports it, we plan to offer both for next year.”
Nelsen said both hybrids offer 3 percent to 5 percent increases in yield above other recently released hybrids. On average, most hybrids produce about 25 percent more yield than conventional varieties.
RiceTec has always focused on improving yields with its new releases but also puts considerable investment into other characteristics. “In years like this with the high temperatures and the rain we’ve had, hybrids have a better defense mechanism in the Gulf states.”
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