Peach rootstocks differ in their growth responses to both high and low root temperatures

This paper examines the hypothesis that both high and low root zone temperatures (RZT) reduce growth in peaches and that peach rootstocks differ in their growth responses to RZTs. This hypothesis was tested by growing plants of five peach rootstocks, Fay Elberta, green leaf Nemaguard, Golden Queen, Okinawa and a redleaf Nemaguard at constant RZTs of 5, 13, 21, 29°C and a diurnally variable RZT of 29/21°C. For the pooled data, over the RZT range 5-29°C, the relationship between RZT and total growth (TG) could be described as bell shaped curve peaking near 21°C, with the mathematical relationship between the two being ln TG = 2.080 + 0.015RZT 2 - 0.0004RZT 3 (r2 = 0.82, p<0.001). The growth of plants whose roots were exposed to the diurnally variable RZT was similar to that of plants exposed to a constant RZT of 29°C; the reduced growth in both groups being attributed to exposure to unfavourable RZTs for part or all of the day. Significant differences in RZT induced growth responses among rootstocks were observed. These trials demonstrate that both sub- and supraoptimal RZTs, independently of air temperature and light intensity, reduce growth and that peach rootstocks differ in their responses to RZTs. This research has implications for future rootstock development and selection, orchard management practices and for the development of models examining peach tree growth and development, particularly with respect to the effects of potential changes in the global climate.