Effect of environmental humidity on the pollen of Capsicum flexuosum, a wild chili pepper from humid climate.

CARRIZO GARCÍA C.

Budapest (Hungría)

Congreso; XIX International Congress on Sexual Plant Reproduction; 2006

International Association of Sexual Plant Reproduction Research

Pollen grains are dehydrated in different degrees when they are ready for dispersal, thus partially hydrated and partially dehydrated pollen are distinguished. Partially dehydrated pollen is in a quiescent state, and it is supposed to be resistant to environmental stresses, while partially hydrated pollen is more active metabolically and more susceptible to environmental changes. Then, pollen viability is related to the environmental relative humidity (RH) and to pollen water retention capacity. High and low RH have shown different effects on pollen viability in several species, surviving better in one condition or the other. Capsicum flexuosum is a wild chili pepper whose reproductive characteristics are still unknown. In Argentina it grows in zones characterized by high temperature and RH (average over 70%). Given the climatic conditions in which this species grows, and the relevance of RH on pollen life, a study of the effect of this environmental parameter was proposed to evaluate how the pollen of this species responds in terms of water content and germinability. Water content was calculated from the volume of pollen fixed in oil. In vitro pollen germinability was calculated as the percentage of pollen germinated in a liquid culture media. In vivo pollen germination was tested on pistils of recently open flowers. Pollen samples were taken from different flowering stages directly from plants grown in a greenhouse, or from flowers kept in the laboratory, to define the pollen features. Besides, pollen from recently open anthers was placed under different RH conditions for 24 hours, when the tests and measurements were performed. Seven RH were created with saturated solutions, namely 7, 22, 32, 55, 75, 85 and 98%. Capsicum flexuosum pollen is tricolporate, has an elliptic contour and low water content (ca. 10%) when it is ready for pollination, after the anthers open completely. Pollen volume (= water content) slightly diminishes from the first (S1) to the third (S3) day of flowering (when the corolla usually closes), and it is almost invariable among RH treatments. However, exine features need further investigation because a change in pollen form is apparent in the highest RH treatments, although the volume change is inconspicuous.             In vitro pollen germinability percentage decreases from 26% in S1 to 23% in S3 in samples taken directly from the plants in the greenhouse. In RH treated pollen, germinability varies between 14 and 15% in RH 32, 55, 75, 85 and 98%, being slightly higher the values registered at 75 and 85%. These values are similar to the germinability percentage obtained for pollen from flowers maintained in the laboratory. Germinability only reaches 5 and 6% after treatments at RH 7 and 22%, respectively. Pollen from all the RH treatments performed is able to germinate in vivo.             The observations made in C. flexuosum indicate that the pollen of this wild chili pepper has the ability to adapt to a wide range of RH (except low levels), as the uniformity of germinability percentages evidences. The insignificant pollen volume variation among treatments may suggest that C. flexuosum pollen may have some mechanisms to control its water content, in spite of the environmental RH level, except at very low percentages, and consequently maintain the ability to germinate.