This study aimed to phenotype young tomato (Solanum lycopersicum L.) plants for heat tolerance by measuring Fv/Fm after short-term heat treatments in climate chambers and selected sensitive (low Fv/Fm) and tolerant (high Fv/Fm) cultivars to investigate their in-field performance. Twenty-eight genotypes were phenotyped at 40:28°C for 2 days in climate chambers. A second screening (four high Fv/Fm and four low Fv/Fm genotypes) was conducted for 4 days at 38:28°C, followed by 5 days’ recovery (26:20°C). The tolerant genotypes maintained high net photosynthesis (PN) and increased stomatal conductance (gs) at 38°C, allowing better leaf cooling. Sensitive genotypes had lower Fv/Fm and PN at 38°C, and gs increased less than in the tolerant group, reducing leaf cooling. Under controlled conditions, all eight genotypes had the same plant size and pollen viability, but after heat stress, plant size and pollen viability reduced dramatically in the sensitive group. Two tolerant and two sensitive genotypes were grown in the field during a heat wave (38:26°C). Tolerant genotypes accumulated more biomass, had a lower heat injury index and higher fruit yield. To our knowledge, this is the first time screening for heat tolerance by Fv/Fm in climate chambers was verified by a field trial under natural heat stress. The differences after heat stress in controlled environments were comparable to those in yield between tolerant and sensitive groups under heat stress in the field. The results suggest that Fv/Fm is effective for early detection of heat tolerance, and screening seedlings for heat sensitivity can speed crop improvement.

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A survey was conducted during June-July 2006 in Chitwan to find out the natural infestation of rice root-knot nematode (Meloidogyne graminicola Golden & Brichfield) in rice nurseries. Thirty nurseries were surveyed and 100 seedlings from each nursery were evaluated. Field survey revealed that M. graminicola was widely distributed in most rice growing areas of Chitwan District. Rice root-knot disease was more prevalent in dry bed condition than wet bed. Most of the farmers grew seedlings in upland (dry) soil and there was more rice root-knot disease and second stage juvenile (J2) population in both nursery soil and seedling root. The galled (diseased) seedlings had significantly shorter roots and shoots. Most of the farmers did not know about the nematode problem and did not follow any management practices to control it in nurseries and/or in the main field. This indicated high risk of multiplication of the nematodes and huge loss in rice production. Thus, it is essential to manage M. graminicola in rice nurseries in order to produce healthy seedlings.

Pot experiment was conducted during July-September 2006 to evaluate some organic amendments such as sesame (Sesamum indicum) biomass, buckwheat (Fagopyrum esculentum) biomass, neem (Azadirachta indica) leaves, chinaberry (Melia azedarch) leaves and chicken manure @ 1, 2 and 3 t ha -1 each against the rice root-knot nematode (Meloidogyne graminicola Golden & Birchfield) in direct seeded rice. The treatments were replicated five times in a randomized complete block design. The number of second stage juveniles (J2) of M. graminicola was significantly low in chicken manure @ 3 t ha -1 . The root knot severity index was significantly low in sesame @ 3 t ha -1 , chinaberry @ 3, 2 or 1 t ha -1 , neem @ 3 t ha -1 and chicken manure @ 2 or 3 t ha -1 amended soil but root lesion severity index was lower only in chicken manure @ 2 t ha -1 treated plots. The fresh shoot weight and length were significantly high in chicken manure amendment @ 2 or 3 t ha -1 at 45 th day after seeding. However, the fresh root weight, length, number of leaves and number of J2 recovered from the roots were non-significant.