Characterization of frost-tolerant plum genotypes (Prunus domestica L.) in Nishabur region, Iran: a morphological and phenological assessment following natural spring frost event

Background: The Nishabur region in Iran is an ancient hub for plum production, home to numerous seedling orchards and indigenous plum varieties. In 2020, an evaluation was conducted in the primary plum-growing zones of Nishabur following a harsh spring frost. Forty-one plum genotypes and local varieties capable of bearing fruit after frost incidents were selected for further examination. These plum selections were evaluated based on 60 morphological, pomological, and phenological traits related to flowers, fruits, and trees, in accordance with the UPOV (2020) plum descriptor.

Results: Among the 41 genotypes evaluated, 35 exhibited high yields, demonstrating their potential as viable options for cultivation in frost-prone areas. The highest coefficient of variation (39.45%) was observed in the fruit color. Several genotypes demonstrated acceptable pomological traits. The genotype 'Kh.Da.cv.04' has the highest values in terms of fruit weight (56.2 g), fruit width (46 mm), and fruit length (61 mm). Significant positive correlations were found between fruit length and leaf length and fruit weight and leaf blade length. Factor analysis revealed that fruit weight, size, and leaf length are the most influential factors, accounting for 52% of the total variance. In the principal component analysis (PCA), genotypes were clustered into four main groups, with 'Kh.Da.s.02' and 'Kh.Da.cv.04' positioned at the positive end of the second axis, separate from the other genotypes. Cluster analysis indicated that these genotypes, along with 'Ha.Bokh.cv.30', formed distinct clusters, considerably distant from the other genotypes, which were grouped into four main clusters.

Conclusions: This research highlights the presence of frost-tolerant genotypes and varieties with suitable environmental adaptability in the Nishabur region, demonstrating relatively acceptable diversity. These genotypes hold potential for breeding and germplasm conservation purposes.