33个苜蓿品种对蓟马的田间抗性比较

为了比较33个苜蓿品种对蓟马的抗性，明确苜蓿品种与受害指数、虫口密度，以及苜蓿株高与虫口密度的关系，作者在第2、3茬苜蓿的营养生长期和初花期对单株蓟马虫口密度进行了调查，并对第3茬苜蓿初花期的受害级别、株高进行了调查，用平均受害指数和模糊聚类法比较了苜蓿品种对蓟马的抗性，分析了平均虫口密度与苜蓿株高及受害指数的关系。结果表明:所有苜蓿品种有虫株率均达100%，不同品种单株平均虫口密度范围为3.15～8.55头/株。以受害指数法评价苜蓿品种的抗性，抗性最高的品种为Brarlfa 53HQ，最感虫的品种为5S43;用模糊聚类法得出抗性最强的品种为Baralfa 421Q，感虫的品种包括5S43;虽然两种比较结果有一定的差别，但总体的趋势趋于一致，模糊聚类法考虑的因素较多，能比较全面地评价苜蓿对蓟马的抗性，其评价结果更为可靠。单株虫口密度与受害指数和株高关系表明，它们均存在明显的曲线关系，虫口密度与受害指数的曲线方程分别为y=(-113.2563+53.6489x)/x，与株高的曲线方程为y=x/(-0.0104+0.0230x)，经χ²检验，这两个方程的拟合程度均很好。

Field comparison of the resistance of 33 alfalfa varieties to thrips

The aim of this study was to compare the resistance of 33 alfalfa varieties to thrips, and to clarify the relationship between population density of thrips and alfalfa plant height and plant damage index. The thrip population of a single branch of each of the 33 varieties was counted during flower development and the main flowering period of the 2^nd and 3^rd alfalfa cuts of a growing season. Plant height and severity of damage to leaves of the sampled branch were also investigated in the primary flowering period prior to the 3^rd cut. Thrip resistance of the alfalfa varieties was compared using a damage index and fuzzy clustering techniques. The relationships between population density of thrips and damage index and plant height were analyzed by regression. All alfalfa varieties carried thrips with thrip density ranging from 3.15-8.55 thrips/head. As assessed by damage index, the most resistant variety was Bararlfa 53HQ, and the least resistant was 5S43. Using Fuzzy cluster analysis, the most resistant variety was Baralfa 421Q, while the least resistant variety was again 5S43. Despite some ranking differences between the two methods, the general conclusions were the same. Since cluster analysis uses population density and damage grade of leaves, it is more suitable for evaluation of resistance. The equation slinking population density and damage index and branch height were, respectively, y=(-113.2563+53.6489x)/x, and y=x/(-0.0104+0.0230x). A chi-square test (χ²) showed the two equations to be related.