Physiological Effects of Saline Water on Two Economically Important Horticultural Crops in South Texas

Abstract

Citrus and watermelons are valuable economic crops worldwide, contributing approximately $120 million combined each year in Texas alone. Both citrus and watermelons are sensitive to saline conditions, which can be problematic in the Lower Rio Grande Valley where they are commonly produced. As Texas increases the percentage of irrigated agriculture each year, and in turn the amount of land potentially exposed to salinization through this practice, grafting salt sensitive plants to tolerant rootstocks becomes a more feasible way to overcome this challenge. Grafting typically improves disease resistance, cold tolerance, yield, fruit quality and has been shown to improve salt tolerance as well. While citrus is commonly grafted to rootstocks that induce desirable qualities in the scion, watermelon grafting is only common in Asia and several European countries due to cost constraints. The main goal of this research was to assess selected rootstocks for salinity tolerance by evaluating plant growth and physiological parameters when subjected to several salinity levels.

In the first experiment, potential sour orange replacement rootstocks C22 and C146 were evaluated for salinity as ungrafted trees and grafted to the Olinda Valencia scion. These trees were then compared to the performance of grafted and ungrafted sour orange trees. The results suggest that C22 and C146 rootstocks are more tolerant to saline conditions than sour orange rootstocks at moderate salinity levels. However, grafting significantly decreased all measured growth and physiological parameters for all rootstocks implying that this scion-rootstock combination may not be ideal. In the second experiment, TAMU mini watermelons were grafted to four rootstocks to determine if any of these would improve their performance when subjected to poor quality irrigation water. Of the four rootstocks and ungrafted TAMU mini watermelon, Strong Tosa showed the most growth when subjected to moderate salinity. Salinity treatments were found to increase fruit quality by increasing the percentage of sugar (brix) and fruit flesh firmness.