November 2014 Plant Health

Disease Discussions: In a Perfect World By A.R. Chase and Margery Daughtrey

ARC: In a perfect world there would be no disease I suppose. My favorite solution would be a way to make the plants resist disease genetically since that is the epitome of biological control. If your wishes could be granted, what do you think is missing from our disease-fighting arsenal?

MLD:Right now I would really like a biocontrol that would make late blight turn tail and run, so that everyone could enjoy organic tomatoes without fear of blight. And I’d like another one that would protect basil from downy mildew. It would be asking too much to have one biocontrol do both jobs — biocontrols are specialists!

ARC: So biological control is increasing in popularity. This is at least partially due to the idea that you can apply something preventatively once and it permanently eliminates disease. None of the products we have available now do that, whether they are synthetic chemicals or biological entities or their “natural” chemicals (biopesticides). Besides the two current problems you list above, what do we need more help with?

MLD:There are so many things still to be conquered. It would be great to have an inoculant that would be able to suppress the effects of Fusarium wilt for the duration of the crop. Growers of cyclamen, chrysanthemum and basil would be at the front of the line to get such a treatment. Chemical solutions are especially poor at Fusarium management, so a stem-dwelling bacterium or fungus that acted to defend the plant would be pretty wonderful. I’m doing all the wishing here … what would you like to see?

ARC: At this point, I would like to see something that really does work on viral diseases. We have a one way street on virus diseases with diagnosis to the dumpster in one quick step. Wouldn’t it be great if we actually could do something either before or after infection that helped with viruses? Something that actually lessens the symptoms without the extreme need to CURE would be good.

How about wishing for even faster, more accurate diagnoses? And it would really make me happy if we even knew what to expect from new genera of ornamentals before we launch into worldwide production.

MLD:Wouldn’t that be great? We certainly are good at bringing in new problems all the time. John Hammond (USDA/ARS Virologist) mentioned at the recent APS meeting (the plant pathologists’ annual meeting) that when we bring in new candidate ornamentals from the wild, from countries all over the globe, the plants can bring a lot of virus baggage within them. Even if those plants are able to tolerate those viruses, sometimes the viruses have the potential to spread to other crops that we are using for food or ornament. And there’s no guarantee that they will be gentle on these new plant hosts. Thinking about roots, what if we had a fertilizer that had just the right nutrients to block the action of root rotters?

ARC: We do know a lot about fertilizer and diseases but I cannot think of anything that would block all diseases, can you? The pathogens all act differently from being very tightly integrated into the plant roots like mycorrhizae to those that live best on already dead or dying roots. Not sure how you could design something to combat the range of things that can happen. It actually makes me think we will eventually find out that unless we stress plants by growing them with too much water, too much fertilizer and no actual soil — they can fight off the diseases themselves. Bet we are actually the ones making all of the problems!