Submitted to: Plant Disease
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/19/2006
Publication Date: 5/1/2007
Citation: Jia, Y., Coarrea-Victoria, F., McClung, A.M., Zhu, L., Liu, G., Wamishe, Y., Xie, J., Marchetti, M.A., Pinson, S.R., Rutger, J.N., Correll, J.C. 2006. Rapid determination of rice cultivar responses to the sheath blight pathogen Rhizoctonia solani using a micro-chamber screening method. Plant Disease. 91:485-489. Interpretive Summary: The fungal pathogen Rhizoctonia solani is a broad host pathogen that infects many agronomically important crops. On rice, it causes sheath blight disease and sheath blight disease is an old disease and has been a serious problem for rice production even since the deployment of semi-dwarf cultivars under intensified high yielding production systems. The development of improved resistant cultivars has been hindered by inefficient screening methods. In an effort to develop a standardized efficient method for determining cultivar susceptibility to R. solani isolates five rice cultivars with known field reactions to the disease were evaluated in a blind test in Arkansas and Texas, USA and CIAT (Cali, Colombia). Rice seedlings were inoculated at 3-4 leaf stage with potato dextrose agar plugs containing mycelium and then covered with a 2 or 3 liter transparent plastic bottle for maintaining high humidity and suitable temperature for R. solani to infect the host. Local isolates of the pathogen were used in the inoculation. Cultivars Jasmine 85 and Lemont that had demonstrated clear resistance and susceptibility, respectively, in previous field and greenhouse studies were used as controls. Concurrent field experiments in Arkansas and Texas were performed to exclude response differences due to variation in the isolates used at the different locations. Consistent results from all test locations indicate that disease reaction of rice to R. solani can be rapidly evaluated in the greenhouse using this micro-chamber method. This micro-chamber method may also be modified to evaluate the disease reactions of a number of agronomically important crops.
Technical Abstract: An accurate greenhouse screening method has not previously been developed to identify host response to sheath blight disease caused by Rhizoctonia solani Kühn that causes significant economic losses in rice yield worldwide. The unavailability of a robust pathometric screening system in the greenhouse has made it difficult to quantify disease reactions to R. solani, and has hampered studies on the genetics of resistance and plant breeding efforts to improve resistance. In an effort to develop a standardized laboratory pathometric micro-chamber screening method to quantify resistance to R. solani in rice, five rice cultivars, representing a wide range of observed disease reactions under filed conditions, were examined in a blind inoculation test at three locations (Arkansas, Texas, and Colombia). Rice seedlings were inoculated at the 3-4 leaf stage with potato dextrose agar plugs containing mycelium and then covered with a 2 or 3 L transparent plastic bottle for maintaining high humidity after inoculation. Two cultivars Jasmine 85 and Lemont that have consistently been demonstrated to show the highest and lowest levels of resistance, respectively, in previous field and greenhouse studies were used as controls. Concurrent field experiments in Arkansas and Texas were also performed to compare the greenhouse disease ratings with those observed under field conditions. Overall, the relative disease ratings of the seven test cultivars were consistent between test locations and with field evaluations. Thus, the micro-chamber screening method can be used as an effective approach to accurately quantify resistance to the sheath blight pathogen under controlled greenhouse conditions and should help expedite the selection process to improve resistance to this important pathogen.