Distribution and phenotypic variation in Juglans regia L. growing in Hindu Kush ranges of Pakistan

Abstract

It has been shown that plant morphology and pomology are shaped by their genotype and respective environmental changes. We hypothesize that climate induces variability in Juglans regia (walnut) landraces growing in the un-explored area of Pakistan. ArcGIS modelling and cartographic functions were performed for the indication of variation in temperature, precipitation, mean diurnal range, humidity and precipitation seasonality. Maxent Modelling techniques were used to determine the most important variables responsible for the current distribution of the species. Among the qualitative traits, Broad elliptic leaf shape and dark green leaf color were dominant traits in all three districts, while Ovate Nut shapes were noted in district Swat and Upper Dir and Broad ovate shapes were recorded in district Lower Dir. For quantitative traits the Pearson correlation revealed that leaf width (LW) showing positive significant correlation with nut volume (NV) (r = 0.24) and nut diameter (ND) (r = 0.199) only in district Swat. Descriptive statistics revealed that nut volume (NV) showed high variation i.e. 32.97% in district Upper Dir & 32.54% in District Lower Dir followed by 10 KW (kernel weight) with 27.26% diversity in district Swat. It was found that, genotypes representing 21.09% nut length (NL) and nut diameter (ND) 10.72% variation while mean value 28.32 and 83.96 respectively with the annual rainfall of 75.15 mm in district Swat, but with gradual increase in rainfall (99.17 mm), genotypes in district Lower Dir contained comparatively smaller nut length (NL) 13.21% and nut diameter (ND) 8.38% variation with mean value 32.93 and 86.38 respectively. Consequently, the genotypes with the smallest nut length (NL) and nut diameter (ND) of 10.71% with the mean value of 30.00 and 7.43% variation with mean value 85.88 respectively were recorded in district Upper Dir where the annual rainfall recorded was 109.75 mm. The regression analysis indicates that rainfall significantly (p ≥ .045 and 0.012) affect the Nut length and Nut diameter with r = −0.99* and r = −1.00*, respectively. It was obvious that, gradual increase in rainfall reduced nut length and nut diameter. The study gives insights in probable effects of environmental variables on the walnut morphology.