Project details: CRDC project ID: MLAB1901

CRDC goal: Click here to select a Goal

CRDC key focus area: Click here to select a KFA

Principal researcher: Dr Maria Manjarrez, Research and Development

Organisation: Microbiology Laboratories Australia

Start date: July 2018

End date: June 2020

Objectives • To verify if the ready to use Test is robust enough to recover infective T. basicola propagules in different soils or farms

• To correlate the levels of T. basicola from field soils or “naturally” infected soils against plant symptoms or disease in cotton

• To determine what other fungi are predominantly involved in causing BRR, if any

Background From the CRDC project 1624 it was concluded that a “ready to use test” selected in that project for quantification of BRR needed to be fine-tuned using “artificially” infected soils. The initial development of the test used one soil type with or without black root rot. The initial quantification using the ready to use test was merely based on the contrasting levels without taking into account what was happening with the plant (disease incidence).

To verify those results, soils with different levels of BRR and with different properties needed to be tested. If the test was robust enough, the end result will be a tool to help reduce the risk associated with the disease.

The test needed also to be adjusted to test for the interaction with other plant pathogens causing root rot as previous results showed that black root rot may be the result of different fungal species acting together to produce the disease. The results may be used to design a multi-species detection test.

Research activities Our team worked with ±50 soil samples with different BRR histories, from different cotton producing regions (Whitton, Hay, Hillston, Griffith, Macquarie, Lachlan, Canargo, etc). Soil samples were used to establish 4 experiments under controlled conditions. In Experiment 1 and 2, trap plants such as green beans, soybean and pansy were used to facilitate and speed up quantification of T. basicola. However, the trap plants used gave variable, unrepeatable results, which made detection of the pathogen unreliable. After adjusting the methodology and by following advice from the CRDC research team, experiments 3 and 4 were setup using Sicot 620 cotton seeds supplied by Cotton Seed Distributors (CSD). Both experiments gave repeatable results when using the ready to use test with some statistically significant data. Statistical correlations were achieved between BRR levels and reduction of cotton seedlings biomass under controlled conditions. The test was also detecting other pathogenic fungi such as Fusarium and Verticillium.

Outputs From the total number of soil samples, results showed that 8 samples had below detectable level or zero colonies, 6 sites had less than 10 BRR/g soil, 8 had 10-30 BRR/g soil, 11 samples had 30-100 colonies and 9 samples had more than 100 colonies (up to 2000)/g soil after the soils were planted with cotton for 6-10 weeks under controlled conditions. T. basicola also varied depending on the “dilution” of the original soil (from 20% to 50%) for each site. The sometimes very high variability between the soil dilutions during the testing made correlations not always significant. However, some important results were obtained.

Our project concluded that the ready to use test can achieve with reasonable accuracy, quantification of T. basicola at very low, intermediate and very high levels in soils from different farms or sites, which have different chemical and physical properties. This conclusion came after results showed statistical correlations (and or linear regressions) between shoot dry weights and BRR levels (P= 0.0003). These mathematical models may be used to help reduce the risks associated with the disease.

In addition, results showed that plant biomass started decreasing at just 30 BRR colonies/g of soil, which is new information that could be used to correlate better with what is happening in the plant. There was not big difference in biomass reduction after 100 BRR colonies/g soil, however some soils showed up to 1500 BRR colonies/g of soil after planting cotton under controlled conditions.

Another important result was the detection of other pathogenic fungi such as Fusarium and Verticillium using the ready to use test. Although there were no significant correlations between the levels of these fungi and the reduction in cotton seedling biomass, results can be used to better manage seedling diseases in such a cases as fungicide management.

Impacts As results showed a mathematical correlation between BRR levels with biomass reduction (and root “quality”), the ready to use test could be used to reduce the risks associated with the disease (at least partially as other factors may be involved in this complex production system). In discussing the results, we see an opportunity for new cutting-edge data analytics to be paired with the mathematical model so it can “learn” to predict the disease incidence better in the near future so farmers can fully take advantage of this tool.

Key publications 1.Participation at Australian Soil Science conference (suspended for 2020) but will be attending in 2021

2.FUSCOM 2020 presentations- Farmers (October) and Scientific (November, 2020)

3.Twitter

4.Honours Project: “Can Trichoderma and Bacillus be used as biocontrol agents against T. Basicola (BRR) in cotton?” An in-vitro study. Fabiel Hernandez-Espinosa. International Student. 2020. He will be presenting at FUSCOM 2020, scientific program.

Appendix 1

Example of Report generated after soil samples were tested using the Ready to use test. One report per soil sample.