Morphogenetic, phenological and metaxenial diversity in male date palm trees

Abstract

Date palm (Phoenix dactylifera L., 2n=2x=36) is an evergreen, mono-cotyledonous and dioecious (2n=36) fruit plant of Arecaceae family which consists of 183 genera and 2600 species. Pakistan stands at sixth position in the world with total production of 524,041 tons. A significant, attention driven but ignored fact i.e. “metaxenia” exists in date palm which is affect of pollen grain on the maternal tissues of fruit. Mostly date palm male trees are propagated through seed which leads towards genetic variations. For enhanced date fruit quality, it is mandatory to have diverse males of superior quality. Morphological and molecular markers are leading tools in diversity estimation of fruit plants. For outbreak, a comprehensive morphological study is needed to assess, characterize and conserve superior male trees for betterment of date industry. Fifty six morphological traits were used to determine phenotypic diversity among male accessions of date palm. Morphological traits like number of aerial suckers (213.13%), number of basal suckers (176.54%), height of basal root cone (113.04%) and length of smallest acanthophyll (64.48%) exhibited high values of coefficient of variation. Rachis length total ranged from 169.5 to 483.5cm for the accessions BR59 and BR33, respectively. Average number of acanthophylls ranged from 3.25 (JG1) to 23 (BR7). Spathe length varied 9.5-66.5 cm in investigated male accessions of date palm. Maximum rachillae number (424.5) was noted in accession JG13. Maximum basal rachillae length i.e. 47.25cm was found in accession JG48. Strong positive correlation was detected in quantitative variables. Qualitative traits manifesting higher coefficient of variation included aspect of pinnae (50.17%), fiber density (40.56%), color of pinnae (35.10%), grown from (29.71%), grouping pattern of pinnae of lower portion of leaf (28.56%), peduncle color (27.29%) and leaf basis (27.29%). The majority of the accessions exhibited spherical and hemispherical crown shape. The dominant rachillae shape in studied accessions was light zigzag. Twenty SSR molecular markers were used for genetic diversity estimation. Reported SSR primers proved effective for detecting polymorphism among selected male date palm accessions. In this study, genetic diversity ranged from 0.3535 to 0.5208, heterozygosity deviated from 0.3438 to 0.5313 and polymorphic information content varied from 0.3093 to 0.4575. The analysis of molecular variance (AMOVA) disclosed that genetic diversity within population variation was 51%, whereas among population it was 49%. STRUCTURE software showed that at K=2 germplasm was distributed in two populations. Morphology and germination percentage of pollen of genetically diverse nineteen male accessions revealed significant differences in pollen length, pollen width, germination percentage and pollen weight. Great variations were observed in the flowering phenology of different accessions. Maximum period of spathe emergence was observed in accession BR2. Pollen of accession BR67 induced greater fruit weight, bunch weight, pulp weight, fruit length, diameter and sugars in two female cultivars as compare to other pollen sources. Keeping in view the significance of date palm, we are hopeful that this study will be useful in identification, characterization and conservation of superior male date palm accessions on the basis of morpho-genetic, phenological and metaxenial variations.