Selection of Pecan Cultivars Aiming to Release Vigorous and Heat Stress Tolerant Rootstocks

With the development of pecan orchards in subtropical regions of Iran in recent years, it is very important to release vigorous and hot weather tolerant rootstocks for grafting. For this purpose, 15 pecan cultivars were evaluated in terms of seed germination rate, seedling growth rate, and summer heat stress damage in 2019-2021 at Safiabad Agricultural Research Center. The cultivars were included ‘GraTex’, ‘Peruque’, ‘Comanche 4M’, ‘10J’, ‘Wichita 6J’, ‘GraKing’, ‘Choctaw’, ‘Apache’, ‘Wichita 7J’, ‘Comanche 5M’. ‘Stuart 2J’, ‘Stuart 4J’, ‘6M’, ‘Mahan’ and ‘Mohawk’. The evaluated traits were seed germination rate, determination of seedling production index per kilogram of seed, seedling height and diameter, and amount of seedling damage due to heat stress. The results showed that ‘Peruque’, ‘Apache’, ‘Mohawk’, and ‘Wichita 7J’ were preferred with the possibility of producing 126, 86, 75, and 74 seedlings per kilogram of seed, respectively. The results of the height and diameter of the seedlings showed that ‘Peruque’, ‘Stuart 2J’, ‘Comanche 5M’, ‘Mahan’ and ‘Apache’ were vigorous. The heat stress was so intense in 2021 that even several decades old and large pecan trees were damaged. Meteorological information of Safiabad station showed that, the temperature was above 45 degrees Celsius for 435 hours in 2021. The results showed that the seedlings of ‘Peruque’ and ‘Apache’ were the most tolerant and ‘GraTex’ and ‘Mohawk’ were very sensitive. According to the evaluation of seedlings of pecan cultivars in the years, 2019 to 2021, ‘Peruque’ and ‘Apache’ for pecan rootstock production are recommended.