Since the first detection in the Dawson/Callide region of Central Queensland in 2012, reniform nematode has become a serious concern for cotton growers and researchers as well. Although reniform is considered one of the major diseases of cotton in the US, it is still considered a minor problem in the Australian cotton industry due to the limited scientific studies of the epidemiology of reniform in the Australian cotton cropping system. This project had a number of objectives to address knowledge gaps and obtain data to understand how the reniform nematode is interacting with cotton plants in Australian soil so that we can improve the management practice.

In this project, large numbers of cotton fields from both NSW and QLD have been monitored every season to confirm the presence or absence of plant-parasitic nematodes, and to provide an indication of possible nematode problems in the field. To understand the ecology of reniform nematode in Australian cotton, three glasshouse pot trials were conducted specifically to assess the vertical movement reniform nematodes in the vertisol soil, host/non-host suitability to different crops for reniform nematode, and effect of different reniform nematode population on growth and yield of different cotton varieties. The genetic diversity of the reniform populations found in different crops including cotton was compared to each other while it was also compared with international isolates. Additionally, three different field trials were conducted during this project period to investigate the effectiveness of seed treatment products (with nematicidal property) and a biological control agent to control the reniform nematode.

The seasonal field survey has provided information about the prevalence and spread of the reniform nematodes in Australian cotton fields. So far, reniform nematodes have been found in the cotton field in Central Queensland only. Early-season deep core samples (2018/2019 season) from different fields in Theodore shows the variable abundance of reniform nematode in the soil profile. In some fields, they were most abundant in the top 30 cm while some fields had a large population in the 30-70 cm below the surface. Interestingly, in some of the fields, the highest population was found at the depth of 70-100 cm below the soil surface. These results clearly show that the reniform can live and survive deep in the soil profile thereby providing a reservoir of nematodes that may reinfest the planting zone when cotton is sown. The vertical movement pot trial confirmed that the reniform nematode can move upward from deeper soil profile in the presence of a suitable host (cotton) once the seedling starts to grow.

The reniform population trial has provided some interesting results on the varietal response of cotton plants. Although all the varieties were treated similarly, reniform had a direct negative effect on growth (shoot biomass) and yield of variety ‘Sicot 714’ while ‘Sicot 746’ and ‘Sicot 748’ were not affected. This indicates the reniform nematode may significantly reduce the crop yield if the number of nematodes in the soil reaches a certain threshold and different cotton varieties may have different thresholds for reniform. The host/non-host trial has provided evidence that the rotation crops such as corn, forage sorghum, grain sorghum, and wheat are non-host of the reniform nematode. These crops were not infested by a reniform nematode, and interestingly, the reniform population in the soil of these crops was dropped to almost zero. Thus, crop rotation using any of these crops would be a good option to manage the reniform population in the field. It would be worthwhile to conduct a detailed field trial to evaluate whether similar results can be achieved in the field.

In the field trials, commercial seed treatment products with nematicidal properties had no effect on the reniform population in the soil. Similarly, another field trial with a biological product containing Bacillus species named FertiLink showed that this product has no effect on the nematode population in the soil.

The genetic diversity study has shown that the reniform nematodes found in different crops across Queensland are not different from each other. Although it is not clear if the nematodes on other crops are virulent to cotton, they may pose a great threat to the cotton field because of the cross-contamination of reniform nematodes from other crops to the cotton field. This study also confirmed that the Australian reniform population is not different than the international population, therefore the management practices from abroad can also be recommended in Australia.

The research results obtained during this project have been widely disseminated throughout the industry through presentations at different conferences and grower’s meetings.