 to speak and talk about some of the research that I've carried out in the course of my PhD thesis. My name is Elaine Goff. I'm a PhD candidate for the Centre for Crop Health here at University of Southern Queensland. And the title of my presentation is Mycorrhizal fungi improve yield biomass and nitrogen fixation by rhizobia, but increase population densities of the root lesion nematode, Pradylencus thornyi in mung bean. So it's a lot to take in in that title, but I'll break down organism by organism and the host crop. So a little bit about information about our mung bean and the production up here in the subtropical grains region. It's a short season high value summer crop. It's been integrated into serial rotations and can take, you know, up to about 70 to 90 days to harvest. So it really is quite quick. And on a good crop, you can get between $1,000 to $1,200 per tonne per hectare. So it's quite lucrative too. Now, unfortunately, it is a host to the plant parasitic root lesion nematode, Pradylencus thornyi. It is also a host to the beneficial arboscular mycorrhizal fungi and a host to brady rhizobium, nitrogen fixing bacteria. So my research was looking at the interaction between these three organisms in mung bean and the implications to mung bean productivity. So a little bit about Pradylencus. So Pradylencus are the root lesion nematodes. You can see a lovely picture here courtesy of Christy Owen here on the right hand side. So Pradylencus, the root lesion nematodes, they enter migratory endoparasite. That means they enter and move into the plant root cells and doing so they kill the cells and they form these characteristic reddish brown lesions on the plant. This has an impact on root efficiency and it reduces the uptake of nutrients and of water to the plant. So you're resulting in plants that look like they've got very poor vigor. They look quite wilted and you can get nutrient deficiencies. Now in our region paddocks were surveyed and in the surveys undertaken, they found that 75% of paddocks had Pradylencus thornei in the soils. So it's quite a big ubiquitous problem in our region. We know that mung bean is a susceptible host to Pradylencus thornei. It can result in year losses and also it can increase the multiplication of the plant parasite in the roots. Now this has a knock on effect to any crop that's going to be grown next in the sequence. If you get high levels of Pradylencus thornei in the soil and in the roots of susceptible crops, you this leads to a greater yield loss. So another bit of information about brady Rhizobium. So we know that mung bean is a nitrogen-fixing legume. It associates with brady Rhizobium and the commercial isolates that people use to inoculate mung bean in the field is CB1015. Surveys were done in 2005 in the region and they found that poor nodulation in mung bean resulted in a poor yield in the yield reduction of up to 50% especially where nitrate levels in the soil were already low and they found that of the mung bean crop surveyed about 50% were poorly nodulated or had a total failure to nodulate and there's lots of implications about why this might happen. It may be the pH of the soil, it may be you know the the level of nitrate in the soil but our hypothesis is potentially poor nodulation. Could it be have a reason in biology? Could it be due to a Pradylencus thornei infestation or could it be due to a lack of our boscular mycorrhizal fungi inoculum in the soil where mung beans grown? So a little bit about our boscular mycorrhizal fungi. These form a beneficial symbiosis with plants. About 80% of terrestrial plants form this symbiosis and it's a really ancient symbiosis. It's believed to have evolved about 450 million years ago. So what happens in this picture at the top here you can see there's these lovely big fat golden spores here. They'll germinate in the presence of a host and the hyphae then enter into the plant root cells and they form these tree-like structures called arbosals which are found in the picture in here it's stained in blue. Now these arbosals they act as that point of exchange between the plant and the fungus. So the plant can actually delegate about 25% of its photosynthase to the fungus in exchange for increased uptake of poorly mobile nutrients like phosphorus and zinc and also increase the amount of water being uptake to the plant. So it's quite a beneficial symbiosis and they both win really. Now in the literature a lot of reports have been done looking at the interaction between AMF and rhizobia and it had the level of positivity of that interaction in legumes. So we wanted to research that interaction in mung bean. Also mycorrhizal fungi have also been known to alleviate biotic stress caused by pathogens like bacteria and fungi and there's a really nice review by Whips in 2004 go through a lot of soil borne bacteria and soil borne fungi and how AMF can actually alleviate some of the disease severity in the plants and it's worthwhile having a look if you're interested. But also AMF can also alleviate biotic stress caused by plant parasitic nematodes. Now in the literature it can there's a bit of controversy sometimes it can decrease the population densities of the nematodes and sometimes it can increase it. We wanted to know what was the interaction in with regards to Pradylencus the root lesion nematodes and if AMF could be used as a biocontrol agent. Just a bit of a brief outline of the mechanisms potentially of this interaction. We know that AMF improves nutrient uptake to the plant. So potentially you may get enhanced tolerance to nematode infestation because of this increased not uptake of nutrients. AMF can also improve the amount of roots being produced in the plants so you can get kind of a damage compensation against the damage caused by the plant parasite. Now there may also be a competition within the plant roots for infection sites in the cortex. They both inhabit this really specialized ecological niche is very very similar in the root cortex. So there could be a competition between them for host photos and fates or for infection sites. We wanted to find out if there was a competition between them. AMF can also alter interactions in the rhizosphere by changing around the abundance and the populations of my certain microorganisms in the rhizosphere and also changing around root exodates in the host plant. And also it can also alter the plant's defense systems. So initially on infection by AMF the plant might perceive it as pathogen and it primes the plant's immune system in what's called a mycorrhiza induced resistance. So they can prime the plant's defense mechanisms to make it more tolerant or resistant to a disease or an nematode infestation. So we wanted to look at the interaction between these three organisms and what we did is we carried out some glasshouse factorial experiments in a split plot design. The first set of experiments looked at AMF and Pradolancus thornei and rhizobia and the second set of experiments we added on some nutrients plant nutrients into the equation. So we had a multifactorial experiment with AMF, pithornia, rhizobia, nitrogen, phosphorus and zinc. We used the cult of our JDU which has got the market share up here for mung bean. We also used a pasteurized vertus salt so that's the soil that we found quite commonly up here in the northern rains region and there's some of the soil chemical properties are listed down below. So what we found the first question what is the interaction between AMF and rhizobia? Well we were getting this beautiful synergistic effect when you have co-inoculation with AMF and rhizobia together. There's a lot of graphs going on in this thing but basically they all tell the same story. If you can see my mouse the black bar is no AMF no rhizobia then you have with rhizobia with AMF and both together. So going through all the parameters that we were looking at we found that AMF and rhizobia co-inoculated together increase the shoot biomass, the seed yield, nodules in the plant and the nodule biomass in the plant and this then had the the implication or the further impact on improving the nitrogen fixation in mung bean. So we were getting when you had AMF and rhizobia together you were getting twice the amount of NDFA so this is the percentage of nitrogen derived from the atmosphere which is a measure of biological nitrogen fixation so we were getting twice the amount going on when we had AMF and rhizobia together compared to rhizobia alone which had further impact on the amount of fixed nitrogen to the plant and the nitrogen uptake and that's the kind of picture we were looking at. This is the synergistic impact here this is AMF and rhizobia that's AMF that's rhizobia and that's nil so you can see this beautiful boost productivity. So it's likely that mycorrhizal fungi could help explain this nodulation failure problem that we've been seeing in mung bean but we haven't taken p-thornii out of the equation. In the first set of experiments we were seeing that p-thornii actually reduced nodule numbers in the plant at six weeks and that had an impact in slightly reducing the amount of fixed nitrogen to the plant and the nitrogen uptake to the plant at 12 weeks. We also found that p-thornii decreased the concentration in the shoot of phosphorus and zinc in plants that were inoculated with AMF and rhizobia and unfortunately we loved AMF and rhizobia and that interaction but AMF actually increased the population density of p-thornii and so what we were finding here in these red boxes is this is the p-thornii at 10 program initial rate of inoculation without AMF that's your back transformed means so it's about 79. When you added AMF you were actually getting this doubling twice the amount of the population density of p-thornii in mycorrhizal mung bean which is not what we wanted to see but that's what we got and we correlated us with mycorrhizal root colonization and the concentration of phosphorus copper and zinc to the plant that's what we initially correlated this response and there was no correlation with root biomass so this initially correlated it to plant nutrition so we kind of wanted to tease that apart a bit more so we did look at plant nutrients and their implications on the multiplication of p-thornii so the second set of experiments as I mentioned before again you were seeing this increase with AMF so this is without AMF this is with AMF in the polka dotted here so you were getting this increase again but when you added nitrogen alone phosphorus or zinc you were getting a decrease in the population densities of p-thornii so the multiplication of p-thornii in the roots it's not based on nutrition and it's not based on root biomass there was also no competition between the organisms so we looked at the percentage mycorrhizal colonization in the roots using the stain there was no p-thornii didn't really affect the mycorrhizal colonization so we need to determine what mechanisms actually involved in causing this multiplication up of p-thornii in the roots it could be something to do with the reduced plant defense systems so there's been a paper published by Frewital in 2018 looking at another species of root lesion nematode Pradylencus neglectus and he looked at populations in wheat and then a mycorrhizal in inoculation reduced these plant defense metabolites in wheat which caused that multiplication there could also be alterations to the rhizosphere that happens with AMF and that possibly is some kind of a way of why how p-thornii is increasing but that remains to be determined okay so um if you are a grower and I've brought some of this research to mung bean growers they they all want to know is how to increase the AMF and you can you can alter the populations of these organisms in the soil through careful crop rotations so by growing a non-host p-thornii but also a crop that increases mycorrhizal fungi like sorghum, linseed, sunflower and pigeon pea you can kind of manipulate the levels of these organisms in your soil now up here fallows play a big role in crop rotations and fallows do reduce the population density of Pradylencus thorneii but AMF is also an obligate bio-troph so it needs a living plant host to survive on so after fallows which can go up from between your six to eighteen months up here um you because it's a summer dominant rainfall it's depending on the summer dominant rainfall um so if they don't get the rains no crops go in so after fallows you'll find the population densities of AMF are actually really low so to build up those populations you can grow mycorrhizal host crops so crops that have um that can they're not too dependent on mycorrhizal for their nutrition or biomass but they can still produce spores or inoculum in the soil for your subsequent crops that are high mycorrhizal dependency so crops like which have low mycorrhizal dependency could be like wheat or barley but that still produce spores for your higher mycorrhizal dependency crops like mung bean also more work and is being done on plant breeding to progress resistance to Pradylencus thorneii and mung bean and then while it is still maintaining those lovely benefits that we see with that association with the mycorrhizal fungi so just a quick conclusion um just wanted to reiterate those points again that AMF and rhizobia act synergistically which improves nodulation nitrogen fixation plant biomass and seed yield um but we have the problem in that AMF also increased Pradylencus thorneii population densities in mung bean which wasn't correlated with nutrition or root biomass we also know that Pradylencus thorneii can alter the nutrition in mung bean like phosphorus and zinc nutrition and reduce the nodulation and our soils are quite low in phosphorus and zinc so if you have further impacts on nutrient deficiencies in mung beans that can that can really play a role into your productivity of mung bean and also um the interactions between these three organisms and then adding in nutrition it can get really quite complex um so I just want to say thank you very much to my supervisory team that's Dr. Kirstie Owen, Professor John Thompson, Dr. Rebecca Zwart, Dr. Anna Marchuk and thanks to the GRDC for a research scholarship and the USQ RTP scholarship, everyone at the USQ crop nematology team, everyone at the Center for Crop Health here in the University of Southern Queensland and the Leslie Research Facility and the DAF for the Glasshouse space um so if you've got any questions um I'd like to hear them please thank you for your time