Resistance in the wild crop relatives Avena macrostachya and Hordeum bogdani to the aphid Rhopalosiphum padi

Abstract

In previous screening tests the two wild crop relatives Avena macrostachya (Bal., ex Coss. et Dur.) and Hordeum bogdani (Wil.) demonstrated a high degree of resistance to the aphid Rhopalosiphum padi (L.). In a choice situation using wild and cultivated oats and barley, alate aphids settled in lower numbers on the wild species. The results were, however, variable in the Avena combination. Nymph production was significantly higher, development time shorter and adult weight higher on the cultivated varieties. From the third instar and onwards the excretion of honeydew was significantly lower on the resistant plants. In general the honeydew contained less than 1% free amino acids although excreta from H. vulgare contained 3.5%. The percentage of free amino acids found in the honeydew was similar for all plant species (5.2-7.6%) except for H. vulgare, on which the aphids excreted 22~ of the amounts ingested. Amino acids excreted in high proportions on all plants included asparagine, ~-aminobutyric acid, glutamic acid, and glycine. Tissue sectioning did not reveal any obvious mechanical barriers to stylet penetration. The potential use of these wild species as sources for aphid resistance breeding in oats and barley is considered.

Aphid fecundity and grassland invasion: Invader life history is the key

“…The primary nutritional challenge faced by aphids is the acquisition of nitrogen from phloem sap in the form of amino acids (Terra 1988). Nitrogen fertilization of a variety of grasses tends to increase the amount and alter the composition of amino acids in phloem, which can, in turn, increase aphid population growth rates (Weibull 1988, Fraser and Grime 1999, Isopp et al 2000. Thus, our result that N fertilization increased plant biomass, tissue %N, and aphid fecundity is concordant with many previous studies (see review in Awmack and Leather 2002).…”

“…This result mirrors field choice tests in which R. padi aphids preferentially colonized the plant species on which they had higher fecundity (Weibull 1988). This result mirrors field choice tests in which R. padi aphids preferentially colonized the plant species on which they had higher fecundity (Weibull 1988).…”

“…In choice tests, aphids were found at significantly higher densities on annual grasses compared to perennials; however, at least a few aphids were found on each of the grass species after 24 hours, indicating that preference for annuals was not complete. This result mirrors field choice tests in which R. padi aphids preferentially colonized the plant species on which they had higher fecundity (Weibull 1988). This incomplete preference is critically important for disease transmission in West Coast grasslands: although annual grasses substantially increase aphid populations compared to perennials, perennial grasses serve as the among-season pathogen reservoir.…”

Constitutive and Induced Differential Accumulation of Amino Acid in Leaves of Susceptible and Resistant Soybean Plants in Response to the Soybean Aphid (Hemiptera: Aphididae)

“…The amino acid composition of the phloem has also been related with aphid host plant resistance. Studies in cereal crops including oats, barley, rice, and wheat have shown that speciÞc amino acids are correlated with resistance to aphids (Weibull 1988(Weibull , 1994Kazemi and Van Emden 1992). Studies in legumes like Vicia faba L. (Holt and Birch 1984) and Pisum sativum (Auclair 1976) suggest a potential role for total content of free amino acids and amino acids composition in aphid resistance.…”

The performance of Rag1 soybeans and their effects on the soybean herbivore community

“…Srivastava et al (1983) found that alanine and γ-aminobutyric acid stimulated feeding behavior in pea aphid, Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae), whereas as several amino acids such as asparagine, cysteine, proline and tyrosine deterred feeding behavior. Amino acid composition has been linked to resistance to aphid species in cereal crops (Weibull, 1988(Weibull, , 1994. Aphids, due to their ability to pierce directly into a phloem sieve element, are able to get to a richer source of nitrogen as compared to chewing herbivores; most of the nitrogen within a plant is associated with defensive compounds and other, unusable maters.…”