Incidence of Aphelenchoides besseyi in Rice in Louisiana and Host Status of the Most Widely Planted Cultivars

Aphelenchoides besseyi, the causal agent of white tip disease of rice, has been considered a minor pest of rice during the past 50 years in the United States. Recently this nematode has been found in a number of quarantine samples in Louisiana and Arkansas. Objectives of this research were to determine incidence of this nematode in commercial seed sold to producers in Louisiana and to determine the host status of major cultivars currently produced in the state. During 2015-2016, a total of 216 seed samples representing 3 medium grain, 18 long grain, and 4 long grain hybrid cultivars were examined for A. besseyi. The nematode was detected in 12% of the samples and the highest incidence occurred on long grain hybrids with 30% of the 63 samples infested. Nineteen-week-duration greenhouse studies were conducted to evaluate reproduction of the nematode and pathogenicity to three medium, three long grains, and three long grain hybrid rice cultivars currently popular in Louisiana. Reproductive values of A. besseyi ranged from 11.9 to 2.9 for medium grain cultivar Jupiter and long hybrid XL 753, respectively. Grain weights of Jupiter, CL 111 and XL 753 plants inoculated with A. besseyi were significantly reduced below those of non-inoculated controls. There were significant reductions in plant height for all cultivars, except the long grain cultivar CL 152. Plant weights of Jupiter, CL 111, CL 152, XL 745 and XL 753 plants were reduced significantly when inoculated with A. besseyi. Germination and seedling growth studies conducted in the laboratory and greenhouse indicated that A. besseyi had a negative effect of 27% on percentage of seeds germinating of medium grain Jupiter. However, the nematode had a significant negative impact of 0.64 on average on the rate of germination for all cultivars except the medium grain Caffey