In pepper, like in all horticultural crops, quality is an important component of marketable yield. Fruit weight, shape, and uniformity are important quality components in pepper (Aloni et al., 1999; Kissinger et al., 2005; Lim et al., 2007; Navarro et al., 2002). In bell peppers, both shape and size are primarily determined at the preanthesis stage (Munting, 1974). Although genetics play a key role, several other factors also determine fruit shape and size during preanthesis, including temperature and carbohydrate availability (Aloni et al., 1999; Tomer et al., 1998).
Low night temperatures (15 °C or lower) negatively affect bell pepper fruit quality. One of the more striking effects of LNT on pepper flower development is an increase in ovary diameter without a concomitant increase in locule number, which results in “swollen” ovaries and malformed fruit (Aloni et al., 1999; Polowick and Sawhney, 1985; Shaked et al., 2004).
As the duration of LNT increases beyond ≈1 week, both the percentage of ovaries that exhibit swelling (Aloni et al., 1999; Polowick and Sawhney, 1985) and the extent of ovary swelling (Cruz-Huerta et al., 2011) increase. Increased source-sink ratio also increases the proportion of swollen ovaries. Flower fresh weight (FW) on defruited pepper plants was three to four times higher than flower FW on fruiting plants, which resulted in swollen ovaries and malformed fruit (Aloni et al., 1999).
The incidence of swollen ovaries in bell pepper resulting from either LNT or high source-sink ratio has also been correlated with increased ovary carbohydrate concentration (Aloni et al., 1999). Under LNT, pepper plants exhibit slower growth rates, resulting in decreased shoot dry weight (DW) compared with plants grown under higher night temperatures (Mercado et al., 1997). The decreased growth rate may be the result of decreased photosynthesis, because night temperatures below 15 °C may decrease ribulose-1,5-bisphosphate regeneration and Pi availability for recycling (Hendrickson et al., 2004a, 2004b) and/or activities of photosynthetic/carbohydrate metabolizing enzymes (Bertamini et al., 2005; Sundar and Reddy, 2000). Tropical crops, including pepper, are especially sensitive to LNT. Bhatt and Srinivasa-Rao (1993) reported that net CO2 exchange rates in pepper were higher at night temperatures of 22 °C compared with 17 °C. However, night temperature effects on photosynthesis have not been studied in relation to ovary swelling in pepper. In some species such as cotton (Gossypium hirsutum) and bean (Phaseolus vulgaris), however, leaves developed under LNT may acclimate to such conditions, resulting in carbon exchange rates as high as in plants growing under higher temperatures (Singh et al., 2005; Wolfe and Kelly, 1992). It is unknown whether pepper leaves developed under LNT undergo acclimation and regain high photosynthetic rates. If so, then similar photosynthetic rates and slower growth rates under LNT may cause excess carbohydrate accumulation in floral ovaries, resulting in swelling and fruit deformation.
Vegetative growth and photosynthetic rates in pepper are also affected by source-sink ratios. In bell pepper, fruiting decreased vegetative growth rates (Bhatt and Srinivasa-Rao, 1989; Hall and Milthorpe, 1978) and increased leaf photosynthetic rates (Cruz-Huerta et al., 2005) compared with defruited plants. Defruiting, which increases the source-sink ratio, increased starch concentration in stems (Hall and Milthorpe, 1978) and the incidence of flower deformation and swollen ovaries (Aloni et al., 1999). In addition, the percentage of swollen flowers was inversely related to the number of growing fruit on the plant and directly proportional to the concentration of reducing sugars and starch in the flowers developed in those plants (Aloni et al., 1999). This suggests that although defruiting may decrease photosynthetic rates, the decreased carbohydrate production may not be sufficient to maintain an optimum source-sink balance. This may lead to greater assimilate accumulation in flower buds on defruited compared with fruiting plants, resulting in ovary swelling and fruit deformation.
Although ovary swelling is favored by LNT or increased source:sink ratio, the interaction between night temperature and source-sink modification on ovary carbohydrate accumulation and swelling has not been investigated. Thus, the hypothesis tested in the present experiment is that ovary swelling—whether resulting from LNT effects on photosynthesis and vegetative growth and/or resulting from fruiting effects on the source-sink ratio—results from increased non-structural carbohydrate accumulation in ovaries before and at anthesis. The objectives were to determine the interaction between night temperature and fruiting on 1) ovary swelling and vegetative growth; 2) leaf net CER and the photosynthetic acclimation ability of leaves to LNT; and 3) soluble sugar and starch concentrations in ovaries at anthesis.
Allen, D.J., Ratner, K., Giller, Y.E., Gussakovsky, E.E., Shahak, Y. & Ort, D.R. 2000 An overnight chill induces a delayed inhibition of photosynthesis at midday in mango J. Expt. Bot. 51 1893 1902
Aloni, B., Pressman, E. & Karni, L. 1999 The effect of fruit load, defoliation and night temperature on the morphology of pepper flowers and on fruit shape Ann. Bot. (Lond.) 83 529 534
Bertamini, M., Muthuchelian, K., Rubinigg, M., Zorer, R. & Nedunchezhian, N. 2005 Low-night temperature (LNT) induced changes of photosynthesis in grapevine (Vitis vinifera L.) plants Plant Physiol. Biochem. 43 693 699
Bhatt, R.M. & Srinivasa-Rao, N.K. 1989 Effect of deblossoming on photosynthesis and dry-matter distribution in bell pepper (Capsicum annuum L) Photosynthetica 23 466 471
Bhatt, R.M. & Srinivasa-Rao, N.K. 1993 Response of bell pepper (Capsicum annuum L) photosynthesis, growth, and flower and fruit setting to night temperature Photosynthetica 28 127 132
Choi, G.W. & Gerber, J.M. 1992 Studies on flower primordium differentiation of bell pepper (Capsicum annuum L.) HortScience 27 644 (abstr.)
Cruz-Huerta, N., Ortiz-Cereceres, J., Sanchez-Del-Castillo, F. & Mendoza-Castillo, M.C. 2005 Biomasa e indices fisiológicos en chile morrón cultivado en altas densidades Revista Fitotecnia Mexicana 28 287 293
Cruz-Huerta, N., Williamson, J.G. & Darnell, R.L. 2011 Low night temperature increases ovary size in sweet pepper cultivars HortScience 46 396 401
Darnell, R.L., Cruz-Huerta, N. & Williamson, J.G. 2012 Night temperature and source-sink effects on overall growth, cell number, and cell size in bell pepper ovaries Ann. Bot. (Lond.) 110 987 994
Hall, A.J. & Milthorpe, F.L. 1978 Assimilate source-sink relationships in Capsicum annuum L. 3. Effects of fruit excision on photosynthesis and leaf and stem carbohydrates Austral. J. Plant Physiol. 5 1 13
Hendrickson, L., Ball, M.C., Wood, J.T., Chow, W.S. & Furbank, R.T. 2004a Low temperature effects on photosynthesis and growth of grapevine Plant Cell Environ. 27 795 809
Hendrickson, L., Chow, W.S. & Furbank, R.T. 2004b Low temperature effects on grapevine photosynthesis: The role of inorganic phosphate Funct. Plant Biol. 31 789 801
Kissinger, M., Tuvia-Alkalai, S., Shalom, Y., Fallik, E., Elkind, Y., Jenks, M.A. & Goodwin, M.S. 2005 Characterization of physiological and biochemical factors associated with postharvest water loss in ripe pepper fruit during storage J. Amer. Soc. Hort. Sci. 130 735 741
Lim, C.S., Kang, S.M., Cho, J.L., Gross, K.C. & Woolf, A.B. 2007 Bell pepper (Capsicum annuum L.) fruits are susceptible to chilling injury at the breaker stage of ripeness HortScience 42 1659 1664
Mercado, J.A., Reid, M.S., Valpuesta, V. & Quesada, M.A. 1997 Metabolic changes and susceptibility to chilling stress in Capsicum annuum plants grown at suboptimal temperature Austral. J. Plant Physiol. 24 759 767
Navarro, J.M., Garrido, C., Carvajal, M. & Martinez, V. 2002 Yield and fruit quality of pepper plants under sulphate and chloride salinity J. Hort. Sci. Biotechnol. 77 52 57
Nederhoff, E.M., Dekoning, A.N.M. & Rijsdijk, A.A. 1992 Leaf deformation and fruit production of glasshouse grown tomato (Lycopersicon esculentum Mill) as affected by CO2, plant density and pruning J. Hort. Sci. 67 411 420
Polowick, P.L. & Sawhney, V.K. 1985 Temperature effects on male-fertility and flower and fruit-development in Capsicum annuum L Sci. Hort. 25 117 127
Shaked, R., Rosenfeld, K. & Pressman, E. 2004 The effect of low night temperatures on carbohydrates metabolism in developing pollen grains of pepper in relation to their number and functioning Sci. Hort. 102 29 36
Singh, B., Haley, L., Nightengale, J., Kang, W.H., Haigler, C.H. & Holaday, A.S. 2005 Long-term night chilling of cotton (Gossypium hirsutum) does not result in reduced CO2 assimilation Funct. Plant Biol. 32 655 666
Sundar, D. & Reddy, A.R. 2000 Low night temperature-induced changes in photosynthesis and rubber accumulation in guayule Photosynthetica 38 421 427
Tomer, E., Moshkovits, H., Rosenfeld, K., Shaked, R., Cohen, M., Aloni, B. & Pressman, E. 1998 Varietal differences in the susceptibility to pointed fruit malformation in tomatoes: Histological studies of the ovaries Sci. Hort. 77 145 154
Van-de-Dijk, S.J. & Maris, J.A. 1985 Differences between tomato genotypes in net photosynthesis and dark respiration under low light-intensity and low night temperatures Euphytica 34 709 716
Venema, J.H., Posthumus, F. & van Hasselt, P.R. 1999 Impact of suboptimal temperature on growth, photosynthesis, leaf pigments and carbohydrates of domestic and high-altitude wild Lycopersicon species J. Plant Physiol. 155 711 718
Wolfe, D.W. 1991 Low-temperature effects on early vegetative growth, leaf gas-exchange and water potential of chilling-sensitive and chilling-tolerant crop species Ann. Bot. (Lond.) 67 205 212
Wolfe, D.W. & Kelly, M.O. 1992 Photosynthesis of Phaseolus vulgaris in relation to leaf nitrogen and chlorophyll accumulation at low growth temperature Photosynthetica 26 475 478