JIA-2018-09

2070 ZHANG Shuai et al. Journal of Integrative Agriculture 2018, 17(9): 2066–2073 3.3. Identification of A . gossypii biotypes Twenty-one haplotypes representing more than 2 individuals were chosen, and a NJ tree was constructed using MEGA Software. Associated with its host plant, 5 biotypes were identified. Type 1 contained 3 haplotypes, including Hap3, which was one of the top 3 most abundant haplotypes (Fig. 2). The host plants of Type 1 were zucchini, kidney bean, and muskmelon, the distinguishing feature was that it included no primary host. Type 2 contained 5 haplotypes, and was collected from 7 host plants. This biotype was rare on host plants except on Chinese prickly ash in April. Type 3 had the most individuals among the 5 biotypes, but only contained 2 haplotypes. Type 3 was collected from 8 host plants, and was abundant on each host plant, with the most abundance on cotton in August. The distinguishing feature of this biotype was that no individual was collected on muskmelon. Type 4 was the most abundant haplotype among the 5 biotypes, and was collected from all 9 host plants. Like Type 3, it was most abundant on cotton in August. Type 5 had the lowest abundance among the biotypes, being found in only 9 individuals collected on Chinese prickly ash and cotton. Individuals collected from S . japonica belonged to Type 3 and Type 4. 3.4. The biotypes of A . gossypii geographic popu- lations The haplotypes of 19 geographic populations collected from cotton fields were analyzed. The Nh ranged from 1 to 5. The average nucleotide diversity and Hd over all 19 populations were 0.0638% and 0.321, respectively. The populations collected from SDLL (Laoling, Shandong Province), HBLZ (Linzhang, Hebei Province), and SDSX (Shanxian, Shandong Province) only had 1 haplotype. The populations collected from SDJX (Jinxiang, Shandong Province) and HNYL (Yanling, Henan Province) had more abundance of haplotypes, with 5 and 4, respectively (Table 2). All geographic populations and Anyang populations on cotton contained Type 3 individuals, 15 geographic populations and Anyang populations on cotton contained Type 4 individuals, 4 geographic populations contained Type 2 individuals, and 1 geographic population andAnyang populations on cotton contained Type 5 individuals (Fig. 4). 4. Discussion A . gossypii may have undergone rapid diversification from the most recent common ancestor, and the population exhibited greater genotypic diversity as a result. Bioassay of laboratory host-transfer experiments was the original method used to confirm A . gossypii biotypes (Guldemond et al. 1994; Liu et al. 2008; Carletto et al. 2009b; Wang et al. 2016). Simple sequence repeat (SSR) markers were another popular method to assess A . gossypii diversity (Vanlerberghe-Masutti et al. 1999; Thomas et al. 2012; Luo et al. 2016). Mitochondrial gene sequence polymorphisms were also used to distinguish A . gossypii biotypes (Carletto et al. 2009a; Wang et al. 2016). Many studies have reported the existence of host-specific A . gossypii biotypes, but a lack of standardization has prevented comparisons of biotypes (Ebert and Cartwright 1997). In a previous study using SSR Wingless-April A B Wingless-May Wingless-November Winged-November Winged-May Winged-September Winged-August 9 (45%) 1 (5%) 1 (5%) 0 (0%) 3 (15%) 2 (10%) 4 (20%) 0 (0%) 2 (9.5%) 4 (19%) 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%) 5 (23.8%) 0 (0%) 0 (0%) 7 (33.3%) 0 (0%) 2 (9.5%) 1 (4.8%) Fig. 3 Venn diagrams of the number of haplotype distribution across different Aphis gossypii populations. A, 3 aphid populations collected on Chinese prickly ash at 3 times. One common haplotypes was Hap1. B, 4 aphid populations collected on zucchini at 3 times. Four common haplotypes were Hap1, Hap3, Hap4 and Hap16. Wingless-April, wingless aphid populations in April; Wingless-November, wingless aphid populations in November; Winged-November, winged aphid populations in November; Winged-May, winged aphid populations in May; Winged-August, winged aphid populations in August; Wingless-May, wingless aphid populations in May; Wingless-August, wingless aphid populations in August.