Management of nematodes and a stalk borer by increasing within‐field sugarcane cultivar diversity

Abstract

The aim of this study was to determine whether an increase in plant diversity could modify the structure of the nematode community in favour of less pathogenic species and whether it affected the lepidopteran stalk borer, Eldana saccharina . Four sugarcane cultivars were planted either singly or as a mixture in the furrow. Nematodes were enumerated when the crops were 6 months old for five successive 10 to 13 month old crop cycles. Results showed that the mixture of cultivars had little significant impact on the overall abundance of the plant-parasitic or free-living nematodes. However, the nematode community structure within the mixture was slightly different to that observed on any single cultivar planted on its own and there was a higher than expected proportion of Helicotylenchus dihystera during the first three crops. With successive crops and in all treatments, there was an overall trend of increasing proportions of Meloidogyne javanica in the nematode community. However, the way that the change in the species-balance occurred in the mixed cultivar plots suggested a resistance to the evolving dominance of M. javanica . These results showed that sugarcane cultivars interacted within the rhizosphere when planted in a mixture because the observed nematode community in the mixture differed from that expected. The level of damage caused by E. saccharina was slightly lower in the mixture than expected from the actual cultivar composition.

Responses of free-living and plant-parasitic nematodes to sugarcane crop in two soils

“…The monoculture effects over long periods of time without tilling the soil may be similar to fallowing (Hornby & Bateman, 1997), with recovery of microfauna in the rhizosphere and the establishment of nematode suppressive mechanisms (Cadet et al, 2007) . The same dynamic may also explain the fact that the cultivation for the 16th year in Re is similar to areas of native vegetation, favoring nematodes sensitivity to disturbance (Ca/ Om) and Mesocriconema which were found at a low frequency in the first year.…”

Chemical interaction between undamaged plants – Effects on herbivores and natural enemies

“…Crop plants, in which breeding has created different genotypes with known pedigrees, are good models for the study of intra-specific plant diversity. Indeed, mixing different genotypes of the same species of crop plant has been shown to reduce the incidence of several damage-causing organisms that use the plants as hosts (Cadet et al, 2007;Mundt, 2002;Power, 1991). It is not known to what extent chemical interactions can explain these findings, however our own research has established that volatile chemical interaction between different barley genotypes affects both aphids and their natural enemies, and this work will be discussed next.…”

“…If the chemical cues mediating the biological interactions are identified, these could be applied as formulations that modify plant or insect behaviour. Although current knowledge is mainly limited to a model system with barley, there is evidence from other agricultural systems that mixing different genotypes of the same plant species can affect organisms that use the plants as hosts (Cadet et al, 2007;Mundt, 2002;Power, 1991). These questions may become more relevant in the future.…”

“…Although interactions in the field are likely to be complex, with potential for competition and underground chemical exchange, this raises the question of whether volatile interactions between barley genotypes can affect aphid behaviour within field crops. This is interesting because mixed cultivar cropping in cereals has been shown to reduce the incidence of fungal pathogens and aphid-borne plant viruses (Mundt, 2002;Power, 1991), and mixing plant genotypes can reduce biotic damage and increase yields (Cadet et al, 2007;Gustafsson, 1953;Tratwal et al, 2007) …”

Volatile Chemical Interaction Between Undamaged Plants: Effects at Higher Trophic Levels

“…In fact, mixing different genotypes of the same species of crop plant has been shown to reduce the incidence of damage-causing organisms that use the plants as hosts (Power 1991;Mundt 2002;Ninkovic et al 2002;Cadet et al 2007). Again, it is not known to what extent chemical signalling is involved in these interactions.…”