Selecting the superior late-leafing genotypes of Persian walnut (Juglans regia L.) using morphological and pomological evaluations

Abstract

Background Late-spring frost is one of the major factors limiting and reducing yield of Persian walnut (Juglans regia L.) in temperate regions, including Iran. Therefore, in the present study, seedling-originated genotypes of walnut were investigated to identify late-leafing genotypes with high-quality kernels for direct cultivation in orchards or as parents in breeding programs. In the first step, the variation of the selected trees was investigated in terms of traits related to phenology, vegetation, and fruit. In the second step, late-leafing trees were identified and their traits related to kernel quality were investigated to identify superior genotypes. Results Strong variabilities were exhibited among the studied genotypes based on the traits recorded. The genotypes showed high variation based on dates of leafing, full male flowering date, and full female flowering date, including very early, early, moderate, and late. After recording the leafing date, 21 late-leaf genotypes were identified and evaluated to select the superiors among them in terms of kernel quantity and quality. Among them, the values of nut-related traits ranged as follows: nut length: 30.12–49.74 mm, nut width: 29.31–37.17 mm, nut weight: 8.77–16.47 g, and shell thickness: 1.15–2.25 mm. The values of kernel-related traits ranged as follows: kernel length: 22.35–35.73 mm, kernel width: 21.79–29.03 mm, kernel weight: 3.22–8.17 g, and kernel percentage: 35.08–53.95%. Conclusions According to the ideal values and situations of commercial characteristics of walnut, twelve promising late-leafing genotypes (No. 9, 13, 32, 33, 72, 77, 78, 82, 83, 86, 92, and 98) were identified and are recommended for cultivation in orchards.

Genome-Wide Identification of the CBF Gene Family and ICE Transcription Factors in Walnuts and Expression Profiles under Cold Conditions

“…As its sister taxon, J. sigillata (iron walnut), is only grown in the southwest of China, these two walnuts are growing sympatric and exhibit strong gene introgressions [ 23 , 24 , 25 ]. A rapid change in the climate can damage the buds, flowers, young stems, and even the entire plant [ 31 , 32 , 33 ]. Climate change also affects the growth of tree species in their distribution region, and in particular, low temperatures affect plant development and growth [ 23 , 30 ].…”

“…However, there is a limitation for pollinating quality and walnut yield in temperate regions where temperatures can plunge rapidly in the period of late spring frost (cold shock), especially in northern areas [ 28 , 29 , 30 ]. This extremely serious climate change can cause damage to the flower buds and even entire plants [ 31 , 32 , 33 ]. Climate change may affect the growth of woody tree species in their distribution region, as low temperatures affect plant development and growth in wild walnuts [ 23 , 30 ].…”

“…Climate change may affect the growth of woody tree species in their distribution region, as low temperatures affect plant development and growth in wild walnuts [ 23 , 30 ]. The developments in whole genome sequencing in walnut and woody species have revealed evidence of cold and chilling stress [ 28 , 31 , 32 , 33 , 34 ] and the genome-wide identification of gene families related to stress studies in Juglans species [ 35 , 36 , 37 , 38 ]. CBF and ICE1, as important transcription factors in response to cold stress, may enhance the cold resistance of plants under low-temperature conditions by regulating the essential functional genes [ 39 , 40 , 41 ].…”