Pollination relations of Lycopersicon esculentum in native and foreign regions.

Many of our important cultivated plants are cross-pollinated in their native habitat; when grown in other areas their pollination relations may present problems of general biological and practical significance. An unstable condition in foreign areas is anticipated since the flowers may be visited by alien pollen vectors or they may not be visited at all. Reproduction may be seriously affected in an obligatorily cross-pollinated plant-for example, alfalfa (Medicago sativa L.) growing in certain areas in California, where seed production seems to be limited by the fact that the flowers are not always visited by insect species that can adequately crosspollinate them (Linsley, 1946). Among plants commonly accepted to be completely self-pollinated, the garden pea (Pisum sativum L.) was recently found to be cross-pollinated to the extent of 3.3 per cent in Peru, a region that is outside the native habitat of this species (Harland, 1948). Again, differences as great as tenfold in rates of natural cross-pollination of the cultivated tomato (Lycopersicon esculenturn Mill.) were found in various localities in California (Rick, 1949). Such variations obviously have great bearing on breeding practices, methods of seed production, and even yields of the agricultural commodities themselves. Surprising variations are encountered even among anemophilous plants-for example, common wheat (Triticum1 vulgare Vill.), which is usually assumed to be highly self-pollinated. Rates of natural cross-pollination as high -as 34 per cent were found in the United States by Leighty and Taylor (1927), and a large number of natural hybrids between cultivated varieties were recognized by Howard et al. (1910) in the Punjab, where they observed that in the dry climate the glumes often opened, thereby exposing the stigmas to wind-borne pollen. The intrinsic pollination relations of a species are often assumed to be the same as those observed under cultivation in foreign areas. The examples of wheat and tomato just cited show how misleading such assumptions can be. The pollination relations, especially of facultatively cross-pollinated plants, in their native habitat can scarcely be predicted from information gained in foreign regions. Although the former relations may have important practical and theoretical bearing, extremely little is known about them. The tomato has been regarded as a highly self-pollinated plant, and until recently all published tests have indicated very low rates of natural cross-pollination in eight stations in the North Temperate Zone, all outside the range of distribution of the genus Lycopersicon (literature reviewed by Rick, 1949). On the other hand, two recently discovered facts hint that rates might be higher in the indigenous region; namely, rates vary greatly within and between localities in California; and L. peruvianum (L.) Mill.* and related species were found to be genetically self-incompatible and consequently dependent upon pollen vectors for their reproduction in nature (McGuire, unpublished). A study was therefore undertaken of the pollination mechanisms of wild and cultivated tomato species in the Andean region where the genus is native. The present report deals only with the study of L. esculentum and a