Varietal responses of sweet pepper (Capsicum annuum L.) to temperature and irradiance. I. Effects on reproductive growth and development

H.Z. Jaafar

Abstract

The growth and development of the young reproductive plants of two varieties of sweet pepper (Capsicum annuum L.) were investigated in relation to differing temperatures (26, 20, 14 + 3 °C) and irradiance combinations (high, low). Emergence of primary flower bud was accelerated as temperature increased from 14 °C to 20 °C and to 26 °C, and from low irradiance (LI ) to high irradiance (HI). Variety Blue Star (BS; a tropical selection) was more responsive to the combination of high temperature (26 °C) and HI (4.9 MJ/m2/d) than Bell Boy (BB; a temperate selection) in the promotion of earlier development of the flower buds. Low irradiance (2.4 MJ/m2/d) delayed bud emergence to a greater extent in BB than in BS, especially at low temperatures. The interaction of high temperatures and HI also hastened anthesis in BS more than in BB. Under the conditions of high temperatures and LI, anthesis of primary flowers was delayed more in BB than in BS. Low temperature (14 °C) retarded flower development in both varieties to an extent that could not be compensated by HI. Both high temperatures and HI enhanced the anthesis of secondary flowers with no varietal response. Both temperatures at 26 °C and 20 °C were equally effective in promoting flower production at HI whilst LI greatly reduced flower production at both 26 °C and 14 °C. Under HI, both varieties consistently produced increased total number of primary and secondary flowers at all temperatures tested. However, flower production was very much reduced under LI for both BB at 26 °C and BS at 14 °C with a corresponding reduced number of both flowers reaching anthesis. The number of primary flowers reaching anthesis was also closely related to total radiation and thermal time. A highly significant relationship existed between the mean total number of flowers reaching anthesis in BS and BB and total irradiance and thermal time. Although the combination of high temperatures and HI accelerated flower development up to anthesis, the abscission of primary flowers increased in both varieties relative to the 20 °C. Complete abscission occurred in both varieties under high temperature-LI conditions.

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