The frequency of drought periods influences the yield potential of crops under field conditions. The change in morphology and anatomy of plants has been tested during drought stress under controlled conditions but the change in physiological processes has not been adequately studied in separate studies but needs to be reviewed collectively. This review presents the responses of green peas, snap beans, tomatoes and sweet corn to water stress based on their stomatal behaviour, canopy temperature, chlorophyll fluorescence and the chlorophyll content of leaves. These stress markers can be used for screening the drought tolerance of genotypes, the irrigation schedules or prediction of yield.

Measurement of physiological traits can be used to monitor plant water status, for irrigation scheduling or to predict the expected yield in open-field production of vegetables. This study evaluates the changes in stomatal conductance, chlorophyll fluorescence (Fv/Fm), relative chlorophyll content (SPAD), and canopy temperature at different stages of development of processing tomato to show their relationships with the yield and quality under well-irrigated, deficit irrigated, and non-irrigated conditions. Under non-irrigated conditions, during flowering with fruit setting and early fruit development the highest canopy temperature, lowest stomatal conductance, and Fv/Fm were measured, while the SPAD value was the highest. Under this condition, the correlation between the SPAD value, fruit weight, and marketing yield was positive, but it was negative with the total soluble solid (°Brix). During flowering with fruit setting, under deficit irrigation conditions a close significant positive correlation was found between the SPAD value and the fruit weight, marketing yield, and vitamin C content of fruits. During this period, under regularly irrigated conditions, the SPAD, Fv/Fm, and canopy temperature related to stomatal conductance. Stomatal conductance had significant influence on yield and quality under non-irrigated and well-irrigated conditions while the SPAD value and canopy temperature had significant influence on under deficit irrigated conditions.

Good water supply practice provides benefits such as water and energy conservation but also alters the quality of yield. These effects of irrigation on yield quantity and quality are widely researched in the case of many plants. In tomato it can affect the soluble solids content positively together with a slight reduction in yield quantity as confirmed by many studies. There are results in the literature regarding its effect on carotenoid composition and lycopene content as well, but the effect on lycopene isomers has not been revealed yet. In this study, we investigated how different water supply levels affect yield quantity and quality, focusing on lycopene components. A two-year open field irrigation experiment with a center pivot capable of variable rate irrigation was conducted on processing tomato. The water supply levels were 100%, 75%, and 50% of ETc (crop evapotranspiration) until the beginning of the ripening stage, calculated by AquaCrop compared to control without regular irrigation. The results suggested that 75% of ETc supplied till the beginning of ripening, was a balanced water supply level regarding yield quantity, soluble solids content and lycopene concentration and yields, such as higher concentration and ratio to total carotenoids. The evaluation of cis-lycopene concentration and ratio to all-trans did not show clear results in the two years.

Tomato fruit ripening is a complex, genetically programmed process that culminates in dramatic changes in texture, color, flavor, and aroma of the fruit flesh. The characteristic pigmentation of red ripe tomato fruit is the result of the de novo synthesis of carotenoids, mainly lycopene and β-carotene, which are associated with the change in fruit color from green to red as chloroplasts are transformed to chromoplasts. The aim of this study was to examine the effect of ripening conditions on color development and antioxidant content. Detached tomato fruit stored at 15 and 30 °C and vine-ripened fruits were studied to characterize the ripening process by Hue (°) index (CIELab color system), which is strongly influenced by the circumstances of ripening. Total polyphenols, ascorbic acid, and lycopene content of tomato fruits were analyzed at the end of the experiment. Changes in the color of fruit stored at 15 °C and vine-ripened fruit showed significantly higher a* compared with fruit stored at 30 °C. Storage temperature influenced positively ascorbic acid and negatively lycopene content, whereas total polyphenols did not show differences among the different ripening conditions.

Lycopene, found primarily in tomatoes, is a member of the carotenoid family and has potent antioxidant capability. The aims of the present study were: 1) to investigate the effect of grafting on lycopene content of tomatoes and 2) to evaluate the effects of different varieties on lycopene content (open-field with supporting-system, open-field with processing varieties) under the same ecological conditions. The effect of grafting on lycopene content was analysed in the case of two varieties, between the years 2001 and 2003. Lycopene content of tomato fruits decreased significantly by grafting. Ten commercial varieties of tomato produced in Hungary were examined for their lycopene content. Lycopene content of tomato turned out to be extremely diverse, and variable (63.0–155.0 mg/kg fresh weight). It was found that the variety of tomato is one of the most important determinants of lycopene content.\u

Three super-sweet corn hybrids (Zea mays L. convar. saccharata) with different ripening characteristics were grown in three water supplies (regularly irrigated, deficit-irrigated, and unirrigated) to examine the spectral reflectance at leaf and canopy levels, leaf area index (LAI) during the stage of development and their relationship with the yield and nutritional quality. Under unirrigated conditions, the plant’s height, diameter, and weight of ears per plants, as well as total carotenoid content of kernels, decreased, SPAD values of leaves, normalized vegetation differential index (NDVI) and LAI were low. The difference in SPAD and LAI was higher between the hybrids during the silking than the tasseling period under water deficiency. Under unirrigated dry conditions, no correlation was found between SPAD, NDVI, and yield. Using deficit irrigation, SPAD measured during tasseling correlated closely with the individual husked ear and the final yields as well as the sugar and carotene contents of kernels. Under this condition, NDVI did not correlate with the yield, but LAI was correlated with the yield and its carotene content. Under deficit irrigated conditions, the 46 to 49 range of SPAD measured during tasseling predicted 23.5 to 26.7 t ha⁻¹ depending on the hybrid, but this range predicted a yield lower by 6.4 to 10.1% during silking.