EFFECTS OF WHITE TIP NEMATODE ON PHYSICAL PROPERTIES OF RICE GRAINS
Physical properties of agricultural crops are important in the design of more efficient milling, planting and harvesting machines, and also for reducing losses and improving safety in post-harvest handling. In this study, some physical properties of paddy rice, including grain length, width, thickness, geometric diameter, arithmetic diameter and sphericity of the grain, and the percentage of broken rice, healthy rice and milling yield were determined at five levels of Aphelenchoides besseyiin 2012 and 2013. Seedlings of Oryzae sativacv. Hashemi, moderately susceptible to white tip nematode, were transplanted to pots and nematodes inoculated at the three- to five-leaf stage. The results showed that moisture content, grain length, thickness, arithmetic diameter, geometric diameter, and sphericity decreased with increasing inoculation level from 0 to 700 nematodes. The percentage of rice in the head, milling yield, and 1,000 grain weight were also decreased (P<0.05) by the nematode. Broken
grain and unfilled grain were increased significantly in 2012 and 2013, respectively, by A. besseyi, but no effect was seen for grain width. Based on these results, white tip nematode could be a significant preharvest factor in
causing high variability in physical properties as well as in reducing the milling quality of rice.