GROWTH-RESPONSES OF 2 SOLANUM SPECIES TO CONTRASTING TEMPERATURES AND IRRADIANCE LEVELS - RELATIONS TO PHOTOSYNTHESIS, DARK RESPIRATION AND CHLOROPHYLL FLUORESCENCE

Potato production in the tropical lowlands during the rainy season is constrained by high temperature and low irradiance. This study examined the effect of these two variables on dry matter production and allocation, using plant growth, leaf anatomy, gas exchange and chlorophyll fluorescence measurements. Plants of two clones, Solanum goniocalyx cv. Garhuash Huayro (GH) and DTO-33, a heat tolerant clone of S. tuberosum × S. phureja, were grown in growth chambers at 33/25 °C or 20/10 °C day/night temperature. At each temperature, plants were grown in either 12 h high irradiance (430-450 μmol m-2 s-1 PAR) or 12 h low irradiance (250-280 μmol m-2 s-1) both with a 6-h photoperiod extension of 6 μmol m-2 s-1. Plants were harvested after 10 d (initial harvest) and after 20 d (final harvest). By the end of the study DTO-33 had produced more dry matter and had tuberized, whereas GH had a greater leaf area ratio (LAR) and specific leaf area (SLA). The highest relative growth rate (RGR) was at low temperature and low irradiance, possibly due to a combination of thin leaves with a large surface area. At the high temperature, low irradiance had the opposite effect, producing the lowest net assimilation rate (NAR) and lowest RGR. Both tuber number and weight were markedly reduced by high temperature. Low irradiance, in combination with high temperature, produced virtually no tubers. Stomatal density, which was greater on GH than in DTO-33, was increased at high temperature. When measured at 30 °C both clones, especially DTO-33, showed heat-adaptation in terms of ability to maintain a high rate of net photosynthesis at 30 °C. Plants grown at high irr-adiance and low temperature had the lowest net photosynthetic rate at 30 °C. Concurrent measurements of chlorophyll fluorescence indicated that only the initial (O) fluorescence parameter was affected. The data confirm the field observation that reduction in potato growth at high temperature can be aggravated by lower irradiance. This reduction is associated with a reduced leaf area and NAR. © 1992 Annals of Botany Company.