ASHS 2015 Annual Conference

Extreme weather conditions can have a detrimental effect on plant growth and development. Partial shade might help plant growth and production by alleviating the negative effects of excess light and heat. To investigate the effect of different light levels on plant growth and production, ‘Sweet Banana’ chili pepper and ‘Celebrity’ tomato plants were transplanted in raised beds in late April 2014, El Paso, TX. Two weeks later, shade cloth at 50% and 70% of light exclusion were installed to provide three light treatments: full sunlight, 50% sunlight, and 30% sunlight. Field plots under full sun had 9.7% and 16% less soil water moisture and 2.4 °C and 3.0 °C higher soil temperature than those under 50% and 30% sunlight, respectively. Leaf temperature in the afternoon was similar among all treatments in both June and July. In August, chili pepper plants under full sun had 2.1 °C and 4.3 °C higher leaf temperature than those under 50% and 30% sunlight, respectively, whereas tomato plants under full sun had 1.4 °C and 1.2 °C higher leaf temperature than those under 50% and 30% sunlight, respectively. Chlorophyll fluorescence indicated that plants of both crops under full sun were more stressed. Both chili pepper and tomato plants under full sun were shorter and smaller than those under 50% and 30% sunlight. Chili pepper plants grown under full sun produced 62% and 115% more number of marketable fruits and had 17% and 67% higher yields than those under 50% and 30% sunlight, respectively. Tomato plants grown full sun produced 21% and 216% more number of marketable fruits than those under 50% and 30% sunlight, respectively. The yield of tomato plants grown under full sun was 26% less than those under 50% sunlight, but 107% higher than those under 30% sunlight. However, the yield for chili pepper and tomato plants grown under full sun and 50% sunlight was not statistically different. In summary, shade cloth at 50% or 70% of light exclusion could alleviate the high light and temperature stress to some extent for chili pepper and tomato plants. However, shade cloth at 50% of light exclusion tended to reduce the yield of chili pepper plants while 70% shade significantly reduced the yield of chili pepper and tomato plants. Further research is needed to confirm if a shading percent less than 50% would help reduce the light and heat stress without reducing yield for both crops.