Differences in responses to flooding by germinating seeds of two contrasting rice cultivars and two species of economically important grass weeds.

Lucy P Estioko,Abdelbagi M Ismail,David E Johnson,Florinia E Merca,Aurora M Baltazar,Berta Miro

doi:10.1093/aobpla/plu064

Abstract

Crop productivity is largely affected by abiotic factors such as flooding and by biotic factors such as weeds. Although flooding after direct seeding of rice helps suppress weeds, it also can adversely affects germination and growth of rice, resulting in poor crop establishment. Barnyard grasses (Echinochloa spp.) are among the most widespread weeds affecting rice, especially under direct seeding. The present work aimed to establish effective management options to control these weeds. We assessed the effects of variable depths and time of submergence on germination, seedling growth and carbohydrate metabolism of (i) two cultivars of rice known to differ in their tolerance to flooding during germination and (ii) two barnyard grasses (Echinochloa colona and E. crus-galli) that commonly infest rice fields. Flooding barnyard grasses with 100-mm-deep water immediately after seeding was effective in suppressing germination and growth. Echinochloa colona showed greater reductions in emergence, shoot and root growth than E. crus-galli. Delaying flooding for 2 or 4 days was less injurious to both species. Echinochloa colona was also more susceptible to flooding than the flood-sensitive rice cultivar 'IR42'. The activity of alcohol dehydrogenase (ADH) and pyruvate decarboxylase (PDC) in rice seedlings was increased by flooding after sowing but with greater increases in 'Khao Hlan On' compared with 'IR42'. The activity of ADH and PDC was enhanced to a similar extent in both barnyard grasses. Under aerobic conditions, the activity of ADH and PDC in the two barnyard grasses was downregulated, which might contribute to their inherently faster growth compared with rice. Aldehyde dehydrogenase activity was significantly enhanced in flood-tolerant 'Khao Hlan On' and E. crus-galli, but did not increase in flood-sensitive E. colona and 'IR42', implying a greater ability of the flood-tolerant types to detoxify acetaldehyde generated during anaerobic fermentation. Confirmation of this hypothesis is now being sought.

Highlights

Abiotic stresses such as flooding and biotic factors such as weed infestation cause considerable reductions in crop productivity worldwide
The third experiment investigated the effect of late flooding compared with the early flooding
Neither shallow nor delayed flooding was sufficient to suppress the growth of barnyard grass species used in this study; flooding with 100 mm of water immediately after sowing was effective with much less inhibitory effect on the growth of the tolerant rice genotype ‘Khao Hlan On’

Summary

Introduction

Abiotic stresses such as flooding and biotic factors such as weed infestation cause considerable reductions in crop productivity worldwide. Flooding the soil during crop establishment can help control most weeds and reduce production cost. This is practical only if the crop can tolerate flooding during germination and early growth. The present paper examines the physiological aspects of this approach for controlling weeds in the rice crop. Weed competition in direct-seeded fields can be intense since both weeds and rice germinate together. Yield losses due to weed competition have been reported to be 3-fold greater in direct-seeded rice than in transplanted rice (Hill et al 1990)

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