Objective To study the geographic variations and trends in growth traits of different Melia azedarach provenances, select appropriate M. azedarach provenances for afforestation in Guangdong Province, and provide the basis for seed allocation.

Method  The provenance test on M. azedarach from 53 provenances was conducted in Zengcheng, Guangzhou. Growth traits including tree height, ground diameter, branch number, trunk shape and crown were measured. The geographic variations, their trends, and their climatic and ecological basis were explored.

Results There were significant differences among provenances for the tested six traits: Height and diameter showed the highest variations with the ranges of 5-280 cm and 1.2-64.0 cm respectively. Except that trunk shape showed a significant level of variation (P < 0.05), the other five traits all showed highly significant differences (P < 0.01). The repeatability of height, east-west crown and south-north crown were above 40%, suggesting that their variations among provenances were relatively more stable compared to other traits. The repeatability of ground diameter was only 29.92%, indicating low stability of the variation. Regarding the geographic variations in growth traits of M. azedarach at seedling stage, the growth rate of the seedlings decreased as the provenances changed from south to north. The provenances which originated from high altitude grew faster compared to low altitude. The growth traits were influenced by multiple factors including longitude, latitude and altitude, among which latitude was the key factor. In addition, there were apparent climatic and ecological characteristics in the geographic variations of growth traits. The seedlings grew faster and had larger biomass for the provenances from areas of higher temperature, higher mean minimum temperature, more sunshine, more precipitation, and lower atmospheric pressure. Based on the growth traits of young forest, the 53 provenances were roughly clustered into six groups with clear geographic structure using NTsys with Euclidean distance of square sum of deviations.

Conclusion Each provenance has obvious geographic variation trend. We can tentatively select provenances 740, 629, 843 and 349 which have rapid growth, large biomass, nice trunk shape and high adaptability for afforestation in Guangdong Province.