A Method to Estimate Field Response to Hydrogen Sulfide Toxicity and Autumn Decline in Rice Cultivars
In Arkansas where nearly 50 percent of the U.S.A rice is produced, hydrogen sulfide (H2S) toxicity causes the primary symptom that mainly include stunted plants with black root rotting and yellowish foliage in some flooded fields where the disorder prevail. In rice fields where H2S toxicity is severe, rice root crowns rot rendering an opportunity for the invasion of weak pathogenic fungi causing a phenomenon called autumn decline or akiochi in Japanese. The symptoms in rice plants are irreversible once the fungal invasion established. With the identification of more rice fields displaying H2S toxicity and autumn decline in the recent five years, we started testing commercial rice cultivars for tolerance to these disorders. In the testing process we faced problem what scale to use. The objective of the study was directed to developing a method that estimates the combined damages from H2S toxicity and autumn decline on rice root mass and root crown. The scale was developed from percentage values collected separately in 2015 on root mass discoloration and root crown damage. The percentage values were first translated to a 0 to 5 and a 0 to 9 scale for root mass discoloration and root crown damage, respectively. A double weight was assigned to root crown damage due to its greater impact on the survival of a rice plant. To combine the damages from the two disorders, a matrixaddition scale was developed to best reflect our field observations. Correlation coefficients were compared between the prior scales and the transformed matrices in matrix-addition scale. Further verification was carried out in a replicated field experiment in 2016. The matrixaddition scale was verified as reliable and useful to assess rice cultivars grown in fields with a history of H2S toxicity and autumn decline in the U.S.A and worldwide. The scale can also be used to estimate responses of other wetland vegetation or crops that may have two related phenomena.