Increasing lodging resistance performance of rice by alternating drought and flooding stress

Abstract: Stem lodging could result in the reduction of rice yield and was easily affected by drought and flooding which were widely used to reduce irrigation water applied by reducing evaportanspiration and catching rainwater. Previous studies found that flooding could decrease the ability of resistance lodging in most cases while drought has the opposite effects. So it seems possible to mitigate the negative effects of flooding by using the advantages induced by drought under rain-catching and controlled irrigation mode. However, how alternate drought and flooding stress affect the ability of resistance lodging, as well as its underlying mechanism for these behaviors has remained elusive. In this study, three field experiments of T1 (slight drought combined with shallow depth of water after rainfall in paddy field), T2 (slight drought combined with deep depth of water after rainfall in paddy field) and CK (conventional irrigation mode for rice which always keep the shallow depth of water in paddy field) , were established to investigate the responses of stem anatomical structure, stem growth indexes and lodging resistance capabilities to the alternate drought and flooding stress as well as to illustrate the lodging resistance mechanisms for rice stalks under rain-catching and controlled irrigation mode. The results indicated that compared with CK, T1 could decrease the basal inter-node length and increase the stem diameters and stem cross section areas, even thought the differences were not significant. Compared with CK, T1 significantly increased the bending cross-section modulus and cumulative damage energy of stems by 12.4% and 9.4%, respectively; according to stem mesostructure of different treatments, the increase of stem wall thickness, vascular bundles numbers and vascular areas together with the compact vascular cells finally resulted in the improvement of the fracture resistance and the decrease of lodging resistance indexes. Whereas, because of the extremely higher depth of water levels after drought stress, the capability of lodging resistance for T2 treatment decreased. The rising or decline of fresh weight above ground was the major reason for the increase or decrease of lodging resistance indexes rather than that of fracture resistance. In conclusion, properly drought stress exposed in the late growth stage of rice could compensate the decrease of lodging resistance capability and could be used to improve the lodging resistance capability of rice stalk under alternate drought and flooding stress. It also suggested that further increasing the depth of water levels after heavy rain in paddy field under the current water-saving mode would not increase the risk of lodging for rice plant.