Effect of pretreatment on pecan nut germination and rootstock production

Abstract

Pecan [Carya illinoinensis (Wangenh.) K. Koch] is a deciduous tree of the Juglandaceae family, native to temperate regions and growing wild in North America. In Italy, pecan trees are cultivated mainly in the southern regions, where the climatic conditions are optimal for their development. However, the area under cultivation is limited and most of the nuts are imported from the USA and Mexico. A major limiting factor for Italian pecan cultivation is the scarcity of rootstocks suitable for local pedoclimatic conditions. To evaluate the effect of stratification on the germination of pecan seeds to obtain rootstocks, seeds of 5 different cultivars were stratified and compared with those not stratified. The results indicated significant differences in nut germination related to stratification treatment and cultivar. In general, stratification process reduced the germination time from on average 50.4 days for untreated seeds to 12.6 days for treated seeds. The Wichita cultivar exhibited the highest germination rate under stratification whereas the lowest values were observed in non-stratified Cape Fare seeds. On average, better seedling development was observed in the first 6 weeks with stratification, while non-stratified nuts showed better seedling development between week 7 and 11. Shawnee and Wichita cultivars particularly benefited from the treatments, showing superior growth metrics values (35.0±7.9 and 34.9±7.8 cm height; 0.5±0.8 and 0.5±0.6 cm diameter, respectively). Cold stratification produced uniform and robust plants, providing nurseries with quality grafting material. Seeds stored at room temperature for two seasons completely lost their viability, rendering them unusable.