4.1.1. Variations of Morphological Traits
Like other fruit crops, blackberries commercial cultivars have narrow genetic back ground making them not only vulnerable against new biotic and abiotic stresses, but also limits breeding programs with lack of variation for important plant and fruit traits in domesticated germplasm5. Acquiring comprehensive information about the genetic diversity and population structure of wild species is a good strategy for identification of superior genotypes to be introduced as new cultivars or promising parents in future breeding programs6. Results of this study revealed that there is high level of genetic variations among and within Iranian wild blackberry species concerning vegetative, phenological and reproductive traits (Table 2). Plants vegetative and reproductive traits, in addition to genetic factor, greatly depended on environment. Usually, species or accessions from the regions that received greater annual precipitation always had greater leaf dimensions23. Ryabova (2007)24 showed a high level of morphological, phenological and genetic variations of wild raspberry and concluded that these variations might be affected by prevailing soil and climatic conditions as well as topography of the location. Furthermore, vegetative traits such as the number of nodes, shoot length, and plant size are depending on light penetration to the plant25. Also, hybridization between close species and changes in ploidy level, could be one reason for the wide range of vegetative trait diversity10.
Ahmed et al. (2014)7 studied the genetic diversity of wild raspberry and reported leaf lengths and leaf widths between 91–124 mm and 94–122 mm, respectively, which were higher than those obtained in this study. Sedighi and Rahimmalek (2015)6 studied the morphological traits of wild R. hyrcanus and reported the range of leaf length, leaf widths, and petiole lengths between 53 to 73 mm, 21.3 to 48.1 mm and 10.9 to 18.7 mm, respectively, which were in accordance but much lower than values recorded in current study. This differences could be mainly due to the higher number of species included and larger geographical area covered in this study compared to their study covering only one species in a limited habitat.
Graham et al. (2003)26 showed that wild R. ideaus population had the range of 21 days for flowering and 65 days for fruit ripening which was much lower than those recorded in this study (79 and 86 days on average, respectively). Also Graham et al. (2009)27 investigated fruit ripening time in different populations of raspberry during 4 years that grown at different locations. They reported that the ripening time was from 21 April to 24 July in 2003, 18 May to 7 July in 2004, 10 May to 23 July in 2005 and 19 May to 6 July in 2006. They expressed this variation were affected by longitude and altitude. In the higher altitude, flowering and ripening dates are later than other areas. Also the cultivated raspberries have completed flowering and fruit set before any of wild populations26. In addition, geographic condition and pollen grain also can effect on flowering and ripening time27.
Some reproductive traits such as fruit size and the number of drupelets (as a yield component) has been a primary objective in all blackberry breeding programs4. Unlike vegetative traits, fruit traits appear to be less influenced by rainfall or elevation. Yilmaz et al. (2009)28 reported the fruits’ length and width in wild populations of R. fruticosus L. ranged from 7.8 to 11.4 mm and 9.4 to 13.0 mm, respectively. Furthermore, they showed fruit weight varied from 0.4 to 1.2 g in wild genotypes. These results are generally in agreement with finding of current research and minor difference may be due to different species and varied number of genotypes in two studies. Maro et al. (2014)8 evaluated genetic diversity of Brazilian raspberry cultivars and showed that fruit length in mountains and plains area ranged from 13.5 to 23.8 mm and 10.5 to 23.5 mm, respectively. Moreover, they reported the fruit diameter ranged from 16.5 to 21.6 mm and 13.8 to 21.5 mm in mountains and plains area, respectively. These differences could be due to higher temperatures in the plains8. The number of drupelets has a direct effect on fruit size and yield and ranged from 50 to 80 drupelets/fruit in commercial cultivars8, that was twice more than that of best genotype studied herein. Various factors can affect the number of druplets in wild genotypes, including pollen source (weakness of pollen grain in wild genotype), pollination, pollinator incompatibility and ploidy level27.
Considering the estimated diversity index (DI), yield and spine density length, leaf length recorded as characteristics having high diversity (DI ≥ 40), while ripening date, leaf width, fruit width, flowering date, fruit, cane length and internode length were categorized as traits having low diversity (DI ≤ 20). Other groups of evaluated characteristics including number of nodes, petiole length, fruit weight, number of fruits/inflorescence, number of drupelets/fruit and number of inflorescences/plant were found to have medium (DI from 20–40) diversity (Table 2).
Maro et al. (2014) 8 studied genetic diversity in raspberry and reported the diversity index of fruit length, fruit width, fruit mass and number of drupelets were 9.63, 7.78, 20.29% and 19.37%, respectively. Singh et al. (2009) reviewed the genetic diversity of wild genotypes in the north-western Himalayan region and reported coefficients of variation for berry weight, berry length, and berry widths were 24.11 g, 13.3 mm, and 11.5 mm, respectively. They concluded that the climatic conditions like temperature, sunlight, rainfall and snowfall can affect these traits. Blackberry yield varied substantially among cultivars as well as from management practices and the locations of production. In floricane blackberry the yield depends on cane number, fruiting laterals per cane, and fruit weight, while in primocane types yield depends on cane number and amount of branching4, 3. Moreover, Weber et al. (2005)29 reported that blackberry yield ranged from 6.8 to 2.6 t/ha which was much more than values recorded in wild genotypes evaluated in current study. They explained the differences between yields as a result of genetics and environmental conditions, which could be affected also by the sensitivity to diseases, pests and the production system29.