Banana root and soil health project - Australia

The banana plant forms an adventitious root system that is dependent on soil physical, chemical and biological properties to function efficiently. A pot experiment demonstrated that increasing soil compaction was able to significantly reduce the weight of banana roots and shoots. However, in the presence of Radopholus similis the effects of soil compaction were obscured, due to the significant reduction in root weight caused by the nematode. The use of a basic set of soil quality indicators that can be readily used by farmers, was linked to soil nematode indicators to determine relationships between soil properties. In a survey of banana fields in North Queensland, different diameter root classes were affected differently by changing soil properties. Banana roots greater than 5 mm diameter were positively correlated with aggregate stability and negatively correlated with soil bulk density. Banana roots less than 1 mm were positively correlated with electrical conductivity. Specific interactions between soil properties become apparent as crop production systems become more uniform. This allows farmers to prioritise management options to improve the most deficient soil health indicators. The addition of organic amendments is one possible method of correcting degrading soils. The use of amendments with high carbon contents, such as grass hay, banana trash and lucerne hay, were able to significantly suppress R. similis in the roots of banana plants relative to untreated soil. Due to banana production being located near environmentally sensitive areas there is an increasing need to monitor and modify soil management practices. However, this needs to be linked with a framework that allows the integration of all soil components with a system to allow continual improvement in soil management to allow banana production to have minimal impact on the surrounding environment

Development of key soil health indicators for the Australian banana industry

To improve the sustainability and environmental accountability of the banana industry there is a need to develop a set of soil health indicators that integrate physical, chemical and biological soil properties. These indicators would allow banana growers, extension and research workers to improve soil health management practices. To determine changes in soil properties due to the cultivation of bananas, a paired site survey was conducted comparing soil properties under conventional banana systems to less intensively managed vegetation systems, such as pastures and forest. Measurements were made on physical, chemical and biological soil properties at seven locations in tropical and sub-tropical banana producing areas. Soil nematode community composition was used as a bioindicator of the biological properties of the soil. Soils under conventional banana production tended to have a greater soil bulk density, with less soil organic carbon (C) (both total C and labile C), greater exchangeable cations, higher extractable P, greater numbers of plant-parasitic nematodes and less nematode diversity, relative to less intensively managed plant systems. The organic banana production systems at two locations had greater labile C, relative to conventional banana systems, but there was no significant change in nematode community composition. There were significant interactions between physical, chemical and nematode community measurements in the soil, particularly with soil C measurements, confirming the need for a holistic set of indicators to aid soil management. There was no single indicator of soil health for the Australian banana industry, but a set of soil health indicators, which would allow the measurement of soil improvements should include: bulk density, soil C, pH, EC, total N, extractable P, ECEC and soil nematode community structure

Root-knot nematode (Meloidogyne javanica) did not affect banana production in subtropical Australia

Root-knot nematodes (Meloidogyne spp.) are thought to reduce growth and yield of banana in the subtropics and that in vitro-propagated plants are more intolerant than those established conventionally from sucker or corm pieces. This paper describes a field trial in subtropical Queensland, Australia, on a site which was naturally infested with spiral nematode (Helicotylenchus dihystera) and inoculated with M. javanica, but where there were no Radopholus similis, Pratylenchus goodeyi or P. coffeae. It compared the effects of M. javanica and H. dihystera on in vitro-propagated and conventionally-grown plants. Inoculation with M. javanica did not affect any parameter of plant growth or yield in the plant crop of either planting type or in the first ratoon of in vitro-propagated plants. However, in the first ratoon crop of plants established as suckers, inoculation with M. javanica reduced numbers of fingers and hands per bunch but did not affect bunch weight. There was no correlation between plant growth or yield and numbers of M. javanica in either planting type in either plant or first ratoon crop, with 0-43 736 M. javanica/100 g root and 0-7940/200 g soil. H. dihystera populations in roots (0-420/100 g) were negatively correlated with growth and yield of the first ratoon of plants established as suckers but positively correlated with growth and yield of plants established as in vitro-propagated plants

New Australian record for Meloidogyne javanica on Portulaca oleracea

Meloidogyne javanica is reported for the first time in Australia on roots of Pigweed (Portulaca oleracea)

Can reniform nematode (Rotylenchulus reniformis) in Australian cotton be managed by crop rotations?

Reniform nematode is an important pest in cotton production in Central Queensland. No reniform resistant cultivars are commercially available. Rotation to resistant or non-host crops is used overseas to manage this pest. The potential of non-hosts to reduce the population density of reniform nematode was investigated in a replicated strip trial over two seasons on a commercial farm in Theodore, Qld. A sorghum plant with biofumigation properties, grain sorghum, and two corn varieties were investigated. In the second year the effect of previous crop on soil population of reniform post-harvest was determined. In the 2014/15 season the four non-hosts significantly reduced soil nematode populations, with reductions of 98% compared with cotton in the top 15 cm of soil post-harvest. Deep coring showed that high populations of reniform were present at depth after cotton, confirming they survive deep in the soil profile. It is possible that re-colonisation of the planting zone could occur by drawing upon this population reservoir. In the 2015/16 season, pre-plant populations in the non-host plots were significantly lower than the cotton plots. Post-harvest however, reniform populations were extremely high in the top profile for all treatments. Fumig8tor forage sorghum was the only crop that significantly reduced the population in the top 15 cm compared to cotton. Soil populations under Fumig8tor were significantly lower than commercial corn 606. Researchers overseas have shown that a single rotation with a non-host may only suppress nematode populations, with economic thresholds being reached again by the end of the next cotton crop. Two successive rotations with a non-host crop are therefore recommended for improved production sustainability in such circumstances. Data from trial concurs, as large populations were observed after cotton for all treatments hence two years out of cotton is not sufficient to manage this pest

Bioassay for enhanced biodegradation of nematicides in soil

In the Australian banana industry, burrowing nematode (Radopholus similis) is controlled by routine use of chemical nematicides, particularly fenarniphos. A loss in efficacy with prolonged use of fenamiphos may be due to enhanced biodegradation by soil microbes. A simple and inexpensive method was developed to test soil for enhanced biodegradation by comparing nematode recovery from unsterile or sterile soil which had been treated with fenamiphos at 10 μ/g soil with nematode recovery from untreated soil. Every 2 weeks, for 8 weeks, corn seedlings were planted in subsamples of the soil and inoculated with R. similis 2 days later. Recovery of R. similis after 7 days from the corn roots was then used as an indicator of enhanced biodegradation. A soil with a long history of fenamiphos application, and reported to contain fenarniphos-degrading microorganisms, reduced the chemical’s active time in unsterile soil to 2 weeks. Some soils which had not previously been exposed to fenamiphos contained microorganisms which rapidly degraded fenamiphos. A soil with enhanced biodegradation of fenamiphos did not prematurely degrade cadusafos. Hence. if fenamiphos is rapidly degraded in soil, rotation with cadusafos may allow nematode management. Comparison of the corn seedling bioassay with a bioassay using Rhizoctonia solani and Aphelenchus avenue confirmed enhanced biodegradation. The corn seedling bioassay is relatively easy to establish and uses the same nematode species which attacks banana plants

Population dynamics and economic threshold of the nematodes Radopholus similis and pratylenchus goodeyi on banana in Australia

To help banana growers to decide when to apply nematicide, economic thresholds were determined for tropical north Queensland, subtropical south-east Queensland and northern New South Wales, Australia. This was done by monitoring nematode populations, root damage and growth parameters of bunching pseudostems in several commercial crops for several years. There was no significant consistent change in the disease index in consecutive years in any of the regions, although there was great variation between crops. However, on two crops in the tropics, the disease index of roots increased. To reduce the risk of not applying nematicide when required, the economic threshold was adjusted down to allow for this increase on some crops. In the tropics with a crop value of $25 000 ha−1 year−1, the economic threshold occurred at a root disease index = 9.2-15.6. In the subtropics with a crop value of$10 000-15 000, the economic threshold occurred at a root disease index = 20.5-35.5. In the subtropics, Radopholus similis (burrowing nematode) was as pathogenic as Pratylenchus goodeyi (lesion nematode) as measured by root necrosis. However, both nematodes were less pathogenic in the subtropics than was R. similis in the tropics. In the subtropics, R. similis tended to be more numerous in warmer months and P. goodeyi in cooler months

The role of varieties and nematicides in controlling plant-parasitic nematodes in isis mill cane supply area

PLANT-PARASITIC NEMATODES (PPN) adversely affect sugarcane productivity. PPN, particularly root-knot nematodes (RKN), are common in sandy soils in the Isis mill cane supply district and have significant impacts on the profitability and performance of ratoons. This study was undertaken to determine the effect of varieties and nematicide treatment on PPN populations and sugarcane productivity. Four varieties, KQ228A, Q183A, Q242A and Q245A, were grown in large commercial strips that were split for +/– nematicide application in the plant cane crop. The effect of nematicide application on PPN populations was short lived (less than five months), whereas populations of PPN were lowest under Q245A and KQ228A for root-knot and lesion nematodes, respectively. This trial demonstrates that there is a potential to refine the current susceptibility classifications to better enable growers and advisors to select an appropriate variety. Copyright © 2018 ASSCT. All Rights Reserved

Bursaphelenchus aff. vallesianus/sexdentati – identification for dying Pinus spp. in Queensland.

Through a combination of geographical isolation, effective quarantine and good fortune, Australia has remained free of many of the known species of forestry nematodes. However, with increasing volumes and sources of traded goods there is increased risk of these species gaining entry. The nematode Bursaphelenchus aff. vallesianus / sexdentati has been recovered from urban and plantation pine trees in Southeast Queensland. This nematode can affect pine seedlings in Europe during heat and drought, and may potentially be associated with pine-wilt disease. The nematode was first detected in a dying tree in suburban Brisbane in July 2014. Wood samples from this tree were collected during response surveillance following emergence of adult Monochamus alternatus (Coleoptera: Cerambycidae) from imported timber pallets. Monochamus alternatus is the vector of pinewood nematode, Bursaphelenchus xylophilus, a major pest of Pinus spp. and cause of pine-wilt disease. Wood samples were soaked for 24 hours and the extracted nematodes examined morphologically. Typical of the genus Bursaphelenchus, the female nematodes were slender, with a fine, but well developed stylet with small basal knobs, slightly off-set head, a large, angular median bulb, longer than wide, the oesophagus overlapping the intestine dorsally and with a posterior vulva at 70-80% of the body length. The female specimens were “hand-picked” and forwarded for molecular analysis at Australian National Insect Collection. The same nematode was subsequently found in NSW and an extensive surveillance program showed it to be widespread across a number of regions throughout the state and also at Passchendaele State Forest, near Stanthorpe, Qld. Molecular identification was confirmed by NSW DPI Plant Health Diagnostic Service. Wood samples from unthrifty host trees will continue to be examined to contribute to our knowledge of the distribution of these nematodes and provide absence data in relation to B. xylophilus, the original target of the QLD surveillance