2019 ASHS Annual Conference

The alkaline pH of the soil and irrigation water in Florida can exacerbate Huanglongbing (HLB) symptoms on citrus. In addition, soil pH of root zone can directly affect nutrient availability and influence root health, and when low/excess can stress root cells through the accumulation of reactive oxygen species. Altogether, optimal soil pH is critical for good performance, and productivity of crops. Although, number of rootstocks that are potentially tolerant to HLB have been released in the past few years, their response to different pH conditions has not been critically evaluated. Thus, understanding the mechanism of high-pH induced damage on citrus is required to minimize existing losses. Therefore, the objectives of this experiment were to understand the effects of different irrigation/soil pH on the performance of commercially used citrus rootstocks and to relate high-pH stress responses with oxidative stress. Seedlings of seven citrus rootstocks: Kuharske citrange, Swingle citrumelo, US-896, UFR-4, UFR-16, US-802, and 46X20-04-6, were chosen for study based on breeder recommendation, commercial use, and prompt availability. Plants were arranged in randomized complete block design (n=8) and irrigated every 2-3 days with sodium phosphate buffers at pH 5.8, 7.0 and 8.0 and with deionized water for control. Plant performance was monitored for a period of 7 weeks. Membrane injury on root tissue estimated through percentage electrolyte leakage was observed to be the least under control conditions and significantly increased with increase in pH from 5.8 to 8.0. Swingle, US-802, and US-896 showed similar nutrient uptake at pH 5.8 and pH 7.0 as explained by the electrical conductivity (EC) readings. However, EC increased significantly with the increase in pH among all the rootstocks. Swingle, Kuharske, and UFR-16 rootstocks had the highest percentage increase in leaf number under control and pH 5.8 treatments and the least under pH 8.0 treatment. US-802, US-896, and 46X20-04-6 rootstocks performed comparably at all three pH ranges and had similar percentage increase in leaf number. All three pH treatments had resulted in similar leaf fresh weight in Swingle, US-802, UFR-16, 46X20-04-6, and UFR 4 rootstocks. pH did not affect root fresh weight among any of the rootstocks which could be due to its effect on light weight-feeder roots. Overall, pH 8.0 was found to be affecting the overall plant growth in most of the rootstocks. Measurement of reactive oxygen species levels and enzyme activity is still underway to understand their role in stress due to high-pH irrigation.