Research On The Development Rule Of Lateral Branch Length And The Molecular Marker Of The Spotted Trait In Melon

Melon is a world horticultural crop and its fruit grows mainly on the lateral branch（especially the first node of lateral branches）.Lateral branch length is an important part of plant architecture in melon.Suitable lateral branch length can improve cultivation management efficiency,photosyhnthate production and product quality.Previous studies on lateral branches in melon focused on the analysis of genetic rule and the mapping of major QTL（Quantitative Ttrait Locus）.This lacked a systematic study on the characteristics of the first node of lateral branches.This study explored development rule,formulated the classification standard,revealed the change trend at the cell levels and studied the genetic pattern on the first node of lateral branches by using two melon materials with difference in the first node length of lateral branches.The localization of major QTL controlling the first node length of lateral branches was preliminarily studied.The main research results were as follows:1.The lateral branches of melon are almost infinite growth.In this study,we measured the first node length of lateral branches at different nodes of main stem for different melon materials and found that the length increased continuously before pollination,and reached its maximum when pollination,then it no longer increased.2.The lateral branches at the 10-15th node of main stem are the main parts for bearing fruit in melon.In order to systematically examine this node length,this study classified it into five grades:extremely short lateral branch,short lateral branch,normal lateral branch,long lateral branch and extremely long lateral branch.In the autumn of 2018 and spring of 2019,the first node length of lateral branches on the10-15th nodes of main stems were measured for M42Se Hua J and M2-182Se materials respectively.The result showed that the length was significantly different in these two seasons,indicating that the lateral branch traits could be inherited stably.The length of lateral branches from M42Se Hua J（female parent）,M2-182Se（male parent）,F₁（crossing between M42Se Hua J and M2-182Se）and F₂generation materials showed that the length of the first node length of lateral branches was inherited as a quantitative trait in these materials.3.The first node of lateral branch of M42Se Hua J and M2-182Se was gotten at 5days before and after pollination（representing the growth and stop-growth stage of the lateral branches）for cross-cutting and longitudinal cutting,and observed the changes in cell level with a microscope.The cell size of M2-182Se with long lateral branch traits was significantly larger than that of M42Se Hua J with short lateral branch traits,showing that the length of lateral branches might be determined by the cell size.4.The molecular marker was not useful to detect the F₂group obtained by the hybridization between M42Se Hua J and M2-182Se because the coincidence rate was only 18.66%in this study.In order to study the QTL in this population,261 pairs primers were screened the polymorphism between the parents,and 16 pairs polymorphic primers were obtained,which were used for 45 lines of F₂generations with obvious length to preliminarily locate the QTL.The result showed that the coincidence rate was generally low.But it prepared for the positioning of the major QTL.The piebald peel is one of the important commercial traits.Molecular marker In Del-spot was developed and used to genotype 20 melon materials.The result showed the compliance rate reached 95%.The In Del-spot marker was further used to identify the spotted or non-spotted trait for 2（F₂）and 5（F₃）population.Among them,the detection accuracy of Qb978（F₂）,Qb931（F₃）and Qb932（F₃）was 96.6%,91.7%and 83.3%respectively.These results showed that the marker had high universality and practicalty.This article comprehensively studied the development rule,genetic charateristics and changes of cell level of the first node length of lateral branches,which had certain significance,and laid the foundation for the gene mapping of the major QTL for the first node length of lateral branches.The development of molecular marker related to the spotted traits in melon provided powerful molecular marker-assisted selection for melon breeding.