Temperature effects on phenological development and yield of muskmelon

Our goal was to construct a simple muskmelon phenology model that could be run with easily obtainable weather station data and used by growers to quan tify phenological development and aid in projecting harvest dates. A growth chamber experiment was conducted with two cultivars of muskmelon ('Gold Ru sh' and 'Mission') to determine how main vine leaf appearance rates respond ed to temperature. We identified three cardinal temperatures for leaf appea rance rate: the base temperature (10 degreesC) at which leaf appearance rat e was zero; an optimum temperature (34 degreesC) at which the rate of leaf appearance was maximal; and an upper threshold temperature (45 degreesC) at which leaf appearance rate returned to zero. Using these three cardinal te mperatures, we constructed a simplified thermal unit accumulator for hourly measurements of air temperature. Main vine plastochron interval (PI), ther mal time to harvest, and final yield were determined for three cultivars of muskmelon ('Explorer', 'Gold Rush' and 'Mission') grown in the field at Ov erton, TX, USA; over six transplanting dates from March to June 1998. PI wa s calculated for each cultivar x transplanting date combination as the reci procal of the slope of main vine node number ns. accumulated hourly thermal units (Sigma Tu). PI was significantly affected by both cultivar and trans planting date. Final yield was sharply reduced in the last two planting dat es. presumably due to high temperature stresses impairing reproductive deve lopment. As air temperatures increased during the field experiment, the lim e interval from transplanting to 10% final harvest was reduced by 21 to 28 d among the three cultivars and the first four transplanting dates. Main Vi ne node number was a useful descriptor of vegetative development for muskme lon.