: The varietal difference of pod dehiscence in 25 soybean cultivars consisting of 16 Japanese and 9 Thai cultivars was examined at 3, 5, 7, 14, 21, 28 and 35 days after placing in a desiccator (desiccator method) and 2, 4 and 7 hrs after placing in an oven at 60ºC (oven-dried method). The cultivars examined were divided into susceptible and resistant groups according to the degree of pod dehiscence. Most of the Japanese cultivars (excepting Suzuotome) and NS1 were susceptible while most of the Thai cultivars (excepting NS1) and Suzuotome were resistant to dehiscence. The degrees of pod dehiscence measured by the desiccator and ovendried methods were nearly the same, and the moisture content of the pods not dehisced was always higher than that of the dehisced pod. The effect of ambient humidity on pod dehiscence was examined in fi ve soybean cultivars SJ5, Shirotae, Tamahomare, CM60 and Fukuyutaka. When the pods were exposed to 15 or 25% relative humidity (RH), the pods of susceptible cultivars, Shirotae, Tamahomare and Fukuyutaka, started to dehisce at 24 hrs after the start of the treatment, but those of resistant cultivars, SJ5 and CM60, did not dehisce for 72 hrs. None of the cultivars dehisced under 50 and 60% RH. These results revealed that placing the pods in the desiccator for 14 days (desiccator method) or exposing the pods to 60ºC for 7 hrs in an oven (oven-dried method) were useful methods for checking the degree of dehiscence.Key words : Desiccator method, Moisture content, Oven-dried method, Pod dehiscence, Relative humidity, Soybean, Strain gauge method, Varietal difference.Pod dehiscence or pod shattering is one of major factors leading to remarkable yield losses in harvesting. Pod dehiscence is a specifi c characteristic observed not only in soybean but also in Brassica species (Meakin and Roberts, 1990;Child et al., 2003), sesame (Langham and Wiemers, 2002), other pulse crops (Weeden et al., 2002) and birdsfoot trefoil (Lotus corniculatus L.) (Metcalfe et al., 1957;Grant, 1996).The pattern of dehiscence reveals that the tissues are under tension. Either natural or mechanical condition stimulates the tissue to separate quickly at specifi c point (Spence et al., 1996). In soybean, mature pods dehisce along both the dorsal and ventral sutures and scatter their seeds under low-humidity conditions (Tsuchiya, 1987). The dehiscence of soybean pods is one of the major constraints on mechanical harvest because the harvest loss increases due to seed scattering. Shattering loss during harvesting of soybean also increases as moisture decreased (Philbrook and Oplinger, 1989). While pods opened, the seeds can be lost during drying. Mechanization of soybean cultivation is limited in some countries (Langham and Wiemers, 2002). Yield losses of soybean due to the dehiscence was estimated to be 53-319 kg ha -1 contributing to 37% of total loss in the South Eastern USA (Philbrook and Oplinger, 1989). Seed losses of 34-99% in susceptible cultivars and delayed harvesting after maturity are often associated wi...
