SELECTION OF HEAT TOLERANT CLONES

The adverse effect of high temperatures on tuber yield and quality is a major obstacle to potato production in hot regions (Ewing 1981). In the Mediterranean region, as well as in subtropical parts of Asia and Africa, potatoes are exposed to high day and night temperatures and a comparatively dry atmosphere. Almost all Solanum tuberosum cultivars from Europe or North America respond to such conditions with a significant loss in tuber yield and quality (Levy 1985). Local breeding of “heat tolerant” cultivars has been necessary to improve potato production in hot regions.

The selection of heat tolerant clones is carried out in the field or in environmentally controlled glasshouses. Should controlled conditions not be available, selections can be made in aphid-proof screenhouses. Avoidance of virus infections is a major obstacle because of the high aphid populations for most of the year.

The inhibition of tuberization by high temperatures is illustrated in Figure 1. Seedlings from open pollinated seeds of Desiree were grown in the field in Israel under 40-mesh screens, seeds were sown on the first day of each month and seedlings examined for tubers 90 days later. Each point on the graphs represents results obtained from 111 to 264 seedlings (Levy 1984).

FIELD EVALUATION OF HEAT AND DROUGHT TOLERANCE

Although potatoes grown in hot, semi-arid conditions are irrigated throughout most of the growing season, they are nevertheless commonly exposed to water stress resulting from high ambient temperatures and low humidity during the spring and summer.