Research advice

[apl]

Hi Everyone,

I am a graduate student studying the use of composts in potato agricultural systems. One aspect of my research focuses on the possibility that compost amendment may help control Rhizoctonia Solani, the fungal pathogen responsible for stem canker and black scurf. Several studies have shown suppression of R. Solani related diseases by composts in other cropping systems.The efficacy of disease control is thought to be related to both the presence of certain microbial populations and the quality of the compost’s organic matter. However, only a small percentage of composts tested seem to suppress R. Solani, the effectiveness of individual composts being difficult to predict. My goal is to find suppressive composts and characterize their organic matter and microbial populations.

I have completed a pilot greenhouse experiment in which I grew potatoes (Yukon golds) in 2 different growing media. One media consisted of peat mixed with perlite and sand. Peat was chosen due to the fact that it has been found to be conducive to soil-borne diseases. In the second media the peat was replaced with compost. I then inoculated both media with R.Solani grown on cracked wheat. I also planted an un-inoculated set of control pots. My seed potatoes had been pre-sprouted in the dark before being planted. Within a week all of my control plants had emerged while none of the infected pots had. After another week plants emerged in the infected pots and showed no signs of stem canker (I was hopeing to rate disease severity as my response variable). When I dug up the infected pots, it seemed that the initial sprouts had been destroyed and new sprouts had grown showing no disease symptoms. I learned later that sprouts exposed to R.Solani can induce a systemic response in the potato plant. Some of the plants were allowed to produce new tubers, and all of the infected pots showed a high incidence of black scurf (sclerotia). I did not see any difference between the two media, so that it appeared the compost was not having any effect on Rhizoctonia.

I also noticed that setting up and running this experiment took up a lot of space and time. It would be difficult to keep performing this assay for all the different composts that I have collected. I have been trying to come up with a smaller assay that I could use to screen composts before doing a full pot trial. My first thought was to see if radish were adversely affected by the Rhizoctonia I was using (I had a paper which suggested that it might work). The fact that they grow from seed (smaller growing containers and greater conformity) and germinate quickly made them attractive. However, it seems the strain of R.Solani I am using (AG3 1AP) is fairly specific to potato.

So I am wondering , and would appreciate anyone's thoughts, if using TPS might be an option. Basically I would repeat the experiment described above using seedling trays, with a variety of different media. I am hoping that the seedlings grown would be susceptible to stem canker and that without the large seed potato this might actually damp off infected plants or even keep them from emerging.

My second question is, does anyone know where I might be able to purchase TPS in any kind of bulk?

I’d like to apologize for the long first post to this forum. Thanks in advance for any help.

Andrew

[Rebsie]

Sounds like an interesting project, Andrew. Welcome to the forum.

I would have thought TPS would be a good way to do the trials on a smaller scale, but I'll leave it to those who know more about stem canker and scurf than I do.

[DarJones]

The problem with TPS is that you would have a large amount of variability in the plants. It might be possible if you could get TPS from a variety known to be susceptible in all possible genetic combinations. That would be difficult but not impossible to achieve.

DarJones

[apl]

Thank you for the replies. Over the last couple of days I have been trying to learn more about TPS, reading this forum (very interesting!) as well as other sources. I have been thinking about the variabilty between plants grown with botanical seed. My thought was that with enough replicates I might still be able to detect a treatment effect. Basically all I need to see is a difference between inoculated media and un-inoculated media to begin with. The level of Rhizoctonia disease in my previous potato assay was very high, so I am hoping that even if there are genetic differences in susceptibilty, most of the sprouts will show some sign of disease.
I ordered a packet of the Zolushka seeds (50 seeds). I figured that it would be easy enough for me to plant some and see what happens. I am hoping to have them planted by the end of this week or early next week. For this pilot I am going to plant 24 seeds in inoculated peat media, 24 in uninoculated peat media. I have an incubator with temp control and grow lights.
Does anyone have any experience with the Zolushka seeds? Any temperature or light recommendations?

Andy

[PatrickW]

Hi Andy,

Tom is the expert on TPS, and you can find a video of him talking about growing them here:

www.patnsteph.net/weblog/2009/11/tom-wagner-on-growing-and-saving-true-potato-seeds-tps/

In terms of light, the more the better. In terms of temp, as long as it's in the range of normal room temp it's probably okay.

[Tom Wagner]

I appreciate anyone coming onto this forum and adding some thoughts. Black Scurf is a good topic for lots of discussion.

I did a lot of copy/paste for future reference and to educate not only myself (I need reminders) but for others especially.

Since I am growing as 100% organic as I can, any control of black scurf or rhizoc is a welcomed subject.

I have grown Zoluska in the past but I have better lines in my opinion. I know little of anyone providing TPS (true potato seed) in bulk. I could if the need is there for thosands of seeds and......... millions if one gives me an advance notice of a year or so.

It would be nice to screen my material for any natural resistance to black scurf either individually as a clone, or as a mixture of TPS of say several hundred clones, with untold numbers of male pollen parents. The fact that Black Scurf is part of the damping off problem is something that I may have already achieved some degree of tolerance over the years when damping off problems ruined many a germination tray.

Two things to say about true seed. If it germinates and emerges without the tip burn of rhizoc...one may have some level of resistance in the enoculated soil with the AG3 1AP strain. The least effective way to test for resistance would be to tranplant the potato seedlings from a clean media into the infected media...as the above ground plants survive the rhizoc then. If the tubers develop the "dirt that won't wash off' sclerotia ....the resistance is not there. Some russets and wild species crosses may do better. There is some evidence that Cardinal does better than say Desiree against Black Scurf and I have the grandparents of Cardinal in much of my germplasm.

Much of my breeding work is with true seed and the tubers thereof. I escape the build-up of the black scurf for that reason. I try to avoid tubers that have black scurf on them and I don't treat my planting stock with any treatment whether chemical or biological.

As i grow more and more tubers from TPS, I have a distinct advantage over regular certified seed growers who have to grow several field year's worth of potatoes before they can sell the tubers for planting stock. The natural infection is out there and most commercial growers treat the heck of of the cut tubers when they plant.

My research is on the margins of efficiency....a lot of work but little to show for it. I do use a complex mix of various compost sources into the planting rows in the field and maybe I am getting some beneficial results, I don't know. I use several mycorrhizal associations, where the fungus colonizes the host plant and supplants the problem fungus. I need to learn more but maybe I already have built up a good foundation for growing potatoes without too much rhizoc and some workable resistance through many years (57) of growing successive generations of seedling lines.

If you don't read the newspapers, books, internet articles and searches you are uninformed; if you do read all of that, you are sadly misinformed. But since I grow each crop of potatoes to select out successes against something like Black Scurf....maybe a have something that is not achieved by what I read or don't read but what I just have! I believe that the twain shall never meet between what a person reads and what a person does.

I live in a climate that fosters rhizoc...cold wet soils. I plant shallow and cover later...no wonder I escape the ravages of rhizoc. Here it is...the middle of June...and the rain keeps coming and the temps are down around 48 and night and maybe 54 at 2:30 in the afternoon. We broke the record for not having a day near 75 all Spring! I still have most of my tuber lines to plant out yet...waiting for dryer and warmer weather...and many hundreds of tomato varieties yet to plant outdoors.

Thinking of which....planting as late as July and digging early after about 45 to 60 days later...I am escaping the worst of the rhizoc season. Everybody brags about how early they got their potatoes in....such foolishness...if they only knew.....



Sorry about all the disjointed quotes as follows but hey.....!

Damping off is the term used for a number of different fungus-caused ailments which can kill seeds or seedlings before or after they germinate.
A number of different fungi cause these problems, including:
• Botrytis, also known as "grey mould".
• Macrophomina phaseoli
• Phytophthora
• Pythium
• Rhizoctonia solani
• Sclerotium rolfsii
• Thielaviopsis

Damping off can be prevented in many different ways, including germination in dryer conditions with better air circulation (but this slows germination), starting seedlings in sterilized soil,

Rhizoctonia solani does not produce spores and is hence identified only from mycelial characteristics

www.umext.maine.edu/onlinepubs/htmpubs/2273.htm one of the better links to black scurf.

To date no variety has been found with immunity to the sprout nipping and stem lesion phase. Some varieties show varying degrees of resistance to formation of sclerotia on tubers.
Plant certified seed free of sclerotia. If more than 20 sclerotia are visible on one side of washed tubers, consider using a different seed source. Tuber inoculum is more important than the soil inoculum as the primary cause of disease. Seed growers should plant only sclerotia-free seed.
Treat all seed! Even if sclerotia are not observed, the tubers could still be infested with mycelium of the pathogen. Large sclerotia are more difficult for seed treatment materials to penetrate. Poor control can be the result of large sclerotia on seed pieces. No seed treatment will compensate for poor seed.
Avoid planting in cold, wet soil because it reduces the rate of sprout growth and is optimum for disease to occur. Cover seed with no more than two inches of soil to promote rapid emergence and less chance for infection of sprouts and stems. A level of resistance to Rhizoctonia infection is imparted to an emerging plant with light interception. Therefore, the faster a plant emerges, the less chance there is for infection to occur.
Practice good rotation and, at a minimum, avoid two consecutive seasons of potatoes on the same land. This reduces both the incidence and severity of the disease. Rhizoctonia does not compete exceptionally well with other microbes in the soil. Increasing the rate of crop residue decomposition and the amount of organic matter in the soil decreases the growth rate of Rhizoctonia.
Residue decomposition releases carbon dioxide, which reduces the competitive ability of Rhizoctonia. Since Rhizoctonia is not an effective cellulose decomposer, soil populations are greatly reduced by competing microflora and less disease is observed with good rotation. As soils become devoid of organic matter, Rhizoctonia becomes a competitor and flourishes. Planting potatoes in low organic matter soils with high Rhizoctonia populations encourages growth of the pathogen and an increase in disease. Different soils and different crops incorporated into the soil have varying effects on Rhizoctonia growth and development.
Potatoes should be harvested as soon as the skin is set so minimal bruising will occur. The percent of tuber coverage with sclerotia increases as the interval between vine kill and harvest is lengthened.
October 1992 www.springerlink.com/content/tn2t4488m438hh63/
Abstract Field and laboratory studies were conducted in 1985–1986 to evaluate the relative severity ofRhizoctonia solani damage among 26 clones and five potato (Solanum tuberosum) cultivars. A test with true potato seeds showed that resistance toR. solani could be identified in two years. One highly resistant line was identified by this method. Moderate degrees of resistance were found in lines from the USDA Potato Breeding Program (BARC) with russet types producing a higher percentage of highly resistant lines than round whites. A laboratory test revealed that apical sprout damage (nipping) was variable within and between lines and that it was an important phase of disease development to measure when determining resistance because of its effects on the resulting plant growth and production of marketable tubers. It was also determined that to accurately define resistance toR. solani in potato, all phases of the disease must be evaluated to insure against resistance “breakdown” at some point in plant development.

Cultural Control:
1. Use seed tubers free of sclerotia.
2. Use a 3-year or longer crop rotation including a grass or cereal green manure such as sudex (sorghum-sudan grass hybrid) or Japanese millet the year before potatoes.
3. Promote quick emergence by planting in warm soil, covering seed pieces with no more than 2 inches of soil and hilling up later. Also, avoid wet soil at planting time.
4. Plow down Brassica green manures that contain high levels of glucosinolates, e.g., ‘Pacific gold’ oriental mustard and ‘Idagold’ mustard.

Materials Approved for Organic Production:
Trichoderma (RootShield®) has shown variable results.

A mustard called ‘Caliente 119’ that has been effective in the Pacific Northwest. His team seeded this as a green manure crop, at 10 lbs./acre, with most plots planted in June. The crop was mowed at flowering and tilled into the ground, so the plant was growing for 30 to 90 days, depending on the plot. Remember, the green part of the plant has to be wounded (macerated, in this case) to signal it to release the compounds.

A significant reduction in black scurf was noted in trials with potatoes the following season. I definitely think that a mustard green manure could fit into many rotations aimed at reducing the incidence of black scurf.

Tom Wagner

[apl]

Tom,
Thank you so much for taking the time to provide so much information. It seems (at least to me) somewhat ironic that I am interested in using TPS to study a disease which is of most concern to certified seed tuber producers. I received the packet of Zolushka seeds today, and hope to have them planted some time next week. My hope is that they are not rhizoc-resistant since I am interested in testing disease reduction due to compost amendment. If they work, i.e. show disease symptoms in a condusive media, my advisor would most likely green light more experiments using TPS. It could be very interesting to test your hypothesis about your seeds being disease resistent due to selection.

I'll post info as I get further along.

Thanks again,
Andrew