Optimization of the Sampling Method for Genetic Variation Survey in Maize Populations Using SSR Markers

In this study, single-plant DNA sampling method, multi-plant leaf-mixing DNA sampling method, and single-plant DNA-mixing sampling method were adopted, to analyze the genetic variations of Meng A population and C population 1 using SSR markers and establish the optimal technological system for analyzing genetic diversity of maize populations. DNA samples in different treatments were amplified using 34 SSR primers which were uniformly distributed in ten chromosomes of maize. Polyacrylamidc gel electrophoresis was performed to analyze the polymorphism information content and genetic similarity coefficient of 60 individuals and compare the numbers of alleles amplified from DNA samples in different treatments. The results indicated that Meng A population and C population 1 both had relatively abundant genetic variations and the established technological system could be applied in researches of maize genetic diversity. Extracting DNA samples from mixed leaves of 12 individuals with five replications is the best sampling method, which could achieve similar results to mixed DNA samples of 12 individuals. This sampling method can be applied to analyze the genetic relationship among a large number of maize populations, which can not only reduce the workload, but also significantly improve the efficiency.

Evaluation of spatial and temporal patterns of insect damage and aflatoxin level in the pre-harvest corn fields to improve management tactics

Spatial and temporal patterns of insect damage in relation to aflatoxin contamination in a corn field with plants of uniform genetic background are not well understood. After previous examination of spatial patterns of insect damage and aflatoxin in pre-harvest corn fields, we further examined both spatial and temporal patterns of cob- and kernel- feeding insect damage, and aflatoxin level with two samplings at pre-harvest in 2008 and 2009. The feeding damage by each of the ear/kernel-feeding insects （i.e., corn earworm/fall armyworm damage on the silk/cob, and discoloration of corn kernels by stink bugs） and maize weevil population were assessed at each grid point with five ears. Sampling data showed a field edge effect in both insect damage and aflatoxin contamination in both years. Maize weevils tended toward an aggregated distribution more frequently than either corn earworm or stink bug damage in both years. The frequency of detecting aggregated distribution for aflatoxin level was less than any of the insect damage assessments. Stink bug damage and maize weevil number were more closely associated with aflatoxin level than was corn earworm damage. In addition, the indices of spatial-temporal association （χ） demonstrated that the number of maize weevils was associated between the first （4 weeks pre-harvest） and second （1 week pre-harvest） samplings in both years on all fields. In contrast, corn earworm damage between the first and second samplings from the field on the Belflower Farm, and aflatoxin level and corn earworm damage from the field on the Lang Farm were dissociated in 2009.