Milton C. Rush, Rangaraj Nandakumar, Xueyan Sha, Donald Groth and Steven D. Linscombe
Jupiter is a high-yielding, early-maturing, short-stature, medium-grain rice variety developed at the LSU AgCenter’s Rice Research Station at Crowley and released for commercial production in 2004. Results from field evaluations conducted in Louisiana from 2002-2006 indicate that Jupiter has good field resistance to bacterial panicle blight, rotten neck blast and sheath blight. Jupiter also appears to be resistant to the physiological disorder straighthead.
Bacterial panicle blight of rice, caused by the pathogen Burkholderia glumae
, has been a serious problem causing seed rot and grain rot on rice in Japan since 1955. It has recently been reported in other rice-producing countries around the world. Research at the Rice Station showed it was the cause of an epidemic of panicle blight and grain abortion on rice in the southern United States in 1995. In Louisiana, the disease causes abortion of florets on affected rice plants, resulting in greatly reduced grain filling and the potential for yield losses as high as 40 percent.
Most commercial rice varieties grown in Louisiana are susceptible to bacterial panicle blight. Years with temperatures exceeding 90 degrees F through 9 p.m. have the potential for epidemic development of the disease in Louisiana and the rice-growing areas in the southern United States. The pathogen is carried on the seed and is widely present in commercial rice seeds. No complete resistance has been identified for this disease anywhere in the world. Recent tests indicate that Jupiter exhibits improved resistance to the disease with yield losses much lower than those of other commercial long-grain varieties and the medium-grain variety Bengal.
Bacterial panicle blight and blast caused devastating yield losses in Bengal in the late 1990s, which helped trigger a rapid reduction of acreage in medium-grain rice. Jupiter overtook Bengal in 2006 as the most planted medium-grain rice variety in Louisiana.
A research program was conducted to confirm this variety’s resistance and assess its yield loss to bacterial panicle blight compared to losses among four susceptible varieties – Bengal, Francis, Trenasse and Cocodrie. Field experiments with yield plots inoculated with B. glumae were conducted at the Rice Station during 2005 and 2006. Jupiter exhibited significant partial resistance with average disease ratings of 3 on a 9-point scale (zero = no disease and 9 = grain mostly destroyed by the disease). See Table 1.
Susceptible varieties had ratings ranging from 7 to 9. Mean yield loss in Jupiter across three tests was 551 pounds per acre compared to mean losses from 1,424 pounds per acre to 2,345 pounds per acre among the susceptible varieties. The variety Trenasse had the maximum disease rating of 9 and yield loss of 7,308 pounds per acre (46 percent). A negative correlation between disease development and yield indicated the yield loss could be attributed to the disease with a high degree of probability. Because effective chemical controls are not yet available for this disease, the high level of partial resistance in Jupiter rice is immediately useful. Jupiter will serve as a source of resistance for use in developing new resistant varieties.
Experiments are being used at the Rice Station to identify pathogen-responsive genes and the molecular basis of partial resistance in Jupiter. Early results show the resistance is due to the expression of certain genes during plant-pathogen interactions. Identifying these genes and their products will explain the basis for the high level of partial resistance. This study will identify the molecular basis of resistance in Jupiter and assist in transferring this resistance to new varieties through conventional breeding or marker-assisted selection. Milton C. Rush
, Professor; Rangaraj Nandakumar, Postdoctoral Researcher, Department of Plant Pathology & Crop Physiology, LSU AgCenter, Baton Rouge, La.; Xueyan Sha
, Assistant Professor; Donald Groth
, Professor; and Steven D. Linscombe
, Professor and Southwest Region Director, Rice Research Station, Crowley, La.(This article was published in the summer 2007 issue of Louisiana Agriculture.)