Quantitative and Qualitative Losses in Yield of Some Rice Cultivars due to White Tip Nematode (Aphelenchoides besseyi) Infection under Egyptian Field Conditions

The influence of white tip nematode, Aphelenchoides besseyi (Christie, 1942) on some morphological, agronomical and grain yield quality traits of some rice cultivars at various growth stages was investigated under field conditions. Two experiments were carried out during 2003 and 2004 seasons at the experimental farm of Rice Research and Training Center (RRTC), Sakha, Egypt. Severe infection was found able to reduce the yield of susceptible cultivar, Giza 171 by 47% in both seasons and its harvest index by 46.2 and 40.4% in 2003 and 2004, respectively. However, nematode infection increased straw yield by 28.8 and 36.1%, unfilled grains/ panicle by 91.4 and 94.3%, unproductive tillers/ m² by 80 and 93% in 2003 and 2004, respectively. Nematode infection also reduced other agronomic traits such as plant height by 30.3 and 26.3%, flag leaf area by 85.2 and 85.4%, 1000-grian weight by 35.2 and 33.6 %, number of tillers/m² by 60.8 and 58.7 as well as the number of panicles/m² by 62.5 and 65.9% in 2003 and 2004, correspondingly. Grain quality was also negatively affected in both seasons whereas hulling was reduced by 14 and 16.9% , milling by 17.2 and 18.5%, head rice% by 9.9 and 12.3%, grain shape by 19.9 and 20.4%. Chlorophyll content in the tip part of infected flag leaf was also diminished by 90 and 95%. The severe losses in flag leaf area and chlorophyll content due to nematode infection was highly significant and positively correlated with the reduction in panicle length, panicle weight and 1000-grain weight. The results of regression analysis indicated that each 1% of white tip nematode infection reflects 0.75 and 0.69% grain yield loss of Giza 171. Also, these results emphasized the high sensitivity of Giza 171 to white tip nematode infection.