Resistance and tolerance of ten carrot cultivars to the hawthorn-carrot aphid, Dysaphis crataegi Kalt., in Poland

Utilizing genetic variation in perennial sorghum to improve host plant resistance to aphids

With growing concerns over the sustainability of conventional farming systems, perennial crops offer an environmentally friendly and resilient alternative for long-term agricultural production. Perennial grain crops provide numerous benefits, such as low input investment, reduced tillage, soil conservation, better carbon sequestration, sustainable yields, and enhanced biodiversity support. Sorghum (Sorghum bicolor) is the fifth most-grown cereal crop grown for food, fuel, and food grain in the world. The development of perennial sorghum offers a substitute for traditional annual sorghum crops by providing long-term environmental, economic, and agronomic benefits. Sugarcane aphid (SCA; Melanaphis sacchari), a phloem-feeder, is considered a major threat to sorghum production. Since its first report in 2013, it caused $40.95 million in losses in South Texas alone by 2015, accounting for about 19% of the total value of sorghum production in the region. In this study, we screened diverse perennial sorghum genotypes using no-choice and choice assays to determine their innate antibiosis and antixenosis resistance levels to SCAs. Based on aphid reproduction and plant damage rating, no-choice bioassay classified the 43 perennial sorghum genotypes into four clusters: highly susceptible, moderately susceptible, moderately resistant, and highly resistant. To further investigate the resistance mechanisms, we selected two genotypes, X999 > R485 (SCA-resistant) and PR376 ~ Tift241 (SCA-susceptible) that showed the greatest variation in resistance to SCA, for subsequent experiments. Choice bioassay results indicated that aphids chose PR376 ~ Tift241 for settlement, whereas no significant preference was observed for X999 > R485 compared to the control genotype. Electrical penetration graph (EPG) results demonstrated that aphids feeding on the SCA-resistant genotype spent significantly less time in the phloem phase than the susceptible genotype and control plants. The identification of SCA-resistant perennial sorghum genotypes will be valuable for future sorghum breeding programs in managing this economically important pest.

Different Host Plants Distinctly Influence the Feeding Ability of the Brown Citrus Aphid Toxoptera citricida

Simple Summary

The brown citrus aphid, Toxoptera citricida, is an important pest of citrus and causes serious damage in the main production areas. Host plant resistance is an environmentally friendly method to manage aphid infestations and is becoming increasingly important as aphids develop greater resistance to insecticides. The aim of this study was to assess T. citricida resistance on seven widespread and common hosts using electropenetrography combined with a population development test. We showed that the feeding parameters of the brown citrus aphid differed significantly depending on the host plants. Toxoptera citricida spent more time in the pathway stage and less time in the phloem stage on Eureka, while the opposite was observed on Yuzu and Rough Lemon. Measurements of population development of aphids showed that on the Eureka, aphids developed more slowly. Our data suggest that different host plants distinctly influence the ability of T. citricida to feed. The brown citrus aphid did not prefer to feed on Eureka Lemon compared to the other six host plants.

Abstract

Piercing–sucking insects are important crop pests, and an understanding of their feeding behavior and population development plays a crucial role in studying insect population dynamics and crop resistance. In our study, we examined the probing behavior of the brown citrus aphid, Toxoptera citricida, using electropenetrography and assessed its population development after 8 days on seven host plants: Yuzu, Citrus junos Sieb. ex Tanaka; Rough Lemon, C. jambhiri Lush.; ‘Luofu’ kumquat, Fortunella margarita Swingle; ‘Olinda’ valencia orange, C. sinensis (L.) Osbeck; ‘Yanxiwanlu’ Ponkan, C. reticulata Blanco; ‘Rohde Red’ valencia orange, C. sinensis; and ‘Eureka’ lemon, C. limon (L.) Osbeck. The results demonstrated that probing by the brown citrus aphid differed significantly according to the target hosts. Toxoptera citricida produced significantly more pathway activities on Eureka than on Rough Lemon and Yuzu. Toxoptera citricida spent more time from the first probe to first salivation into phloem sieve elements on Eureka compared to Yuzu. In addition, the total duration of ingestion from sieve cells of each aphid in the phloem-feeding phase was shortest on Eureka, and this was significantly shorter than that on Yuzu, Rough Lemon, Luofu, and Olinda. The population number of T. citricida on Eureka after 8 days was significantly lower than that on the other hosts. Overall, Eureka was found to have obvious resistance to T. citricida, whereas Yuzu and Rough Lemon were susceptible host plants. These results provide a theoretical basis for exploring aphid-resistant fruit tree resources using resistant varieties.