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Why High-quality Potato Seed is Important

Expert views on best management practices in potato production.

What’s the secret to a great potato crop? Things like fertile soil, ideal weather and a benign summer free from pests and diseases certainly come to mind, but there’s one crucial factor that sometimes overlooked — starting off with good quality seed.

For this edition of Roundtable, Spud Smart gathered some expert opinions on why it’s important for commercial potato growers to seek out the best seed they can get their hands on and then make sure it’s managed properly.

Our four experts are:

  1. Shawn Paget, who grows potatoes for the french fry and chip sectors at Riverview Farms in Simonds, N.B. He’s also chair of Potatoes New Brunswick.
  2. Gary Hawkins, McCain Food’s director of global variety innovation who’s based in Florenceville-Bristol, N.B.
  3. Loretta Mikitzel, a potato physiologist with the New Brunswick Department of Agriculture, Aquaculture and Fisheries. This past winter, she’s delivered presentations focusing on seed handling and tuber yield at a number of Canadian potato conferences.
  4. Rick Peters, the Agriculture and Agri-Food Canada research scientist in Charlottetown, P.E.I., who’s one of Canada’s leading experts on potato diseases.

Starting Right

The experts agree that when it comes to producing a good potato crop, the importance of starting with high-quality seed cannot be understated.

“It all starts at the beginning, because you have to have good seed in order to get a good crop. If you don’t have good seed, you won’t have good plant health and you won’t get a good yield,” says Paget.

“The seed is your first step of many, and if you mess up with this step with poor seed or poor management of the seed, it haunts you all summer long. You just can’t make up the difference.”

Hawkins agrees: “If something’s not right with the seed, it’s really hard to fix anything else you do downstream — the yield is immediately compromised, and the quality of the crop is potentially compromised. So there’s nothing you can really do to compensate for poor seed.

“If you don’t start with good seed, the consequences are that you won’t get maximum productivity out of the crop and out of all of your inputs. The fertilizer and crop protection products just won’t be as cost-effective, and you can expect your yield to be impacted negatively [as well].”

Mikitzel maintains that starting the season with poor seed is something that can’t be overcome with any amount of fertilizer or fungicides or insecticides. “If you have poor-quality seed, you’re going to have a poor plant stand, and that means you’ve wasted your fertilizer because, say you only get 80 per cent stand, 20 per cent of the ground that you put your fertilizer on is not growing potato plants,” she says.

“Then when you spray your fungicides or your herbicides, you’re spraying bare ground instead of spraying plants, so you’re wasting money there as well. Also, your yield is not optimal. You’ll get 20 per cent fewer plants that are producing yield for you, and then the grade will also be off.”

According to Paget, “It all boils down to plant stand. If you only end up with 80 per cent plant stand because something was wrong with the seed you’re using, you’ve already lost the potential of 20 per cent of your yield at the other end.”

Bruised seed potatoes peeled to show fusarium dry rot infection. Photo: Loretta Mikitzel, N.B. Dept. of Agriculture.

Bruised seed potatoes peeled to show fusarium dry rot infection. Photo: Loretta Mikitzel, N.B. Dept. of Agriculture.

 

Role of Disease

How is high-quality seed determined? The prevalence of disease, whether it’s fungal, bacterial or viral, certainly comes to mind since this plays such a prominent role in how regulators assess potato seed lots.

“The way seed potatoes are assessed in Canada and most parts of the world is they’re inspected the year before [planting] by government inspectors and determined to have at least a minimum level of quality. The less disease obviously the better, and they have to meet certification standards or they won’t be certified for planting the next year,” says Hawkins.

“There’s post-harvest testing in addition to the growing crop inspection, and the post-harvest test is really the most important indication of what that particular seed crop is going to be like the year it’s going to be planted.”

Mikitzel says any time there’s disease in a seed lot, this affects plant vigour. “The more disease you have, the less vigourous plant you’ll get,” she says, adding this can lead to less uniform tuber sizes (caused by erratic plant emergence) as well as more internal and external defects, all important grade considerations.

Peters notes seed potato decay caused by various pathogens can have a significant impact on crop emergence, vigour and ultimately yield. Some, like fusarium spores that are present in most potato fields, can have a lasting impact on seed starting at harvest.

“At harvest time you can get nicks and cuts on your tubers going into storage from the harvest and handling process, and those … wounds allow fusarium to enter,” Peters explains.

He adds that an infection that’s quite small to start with can develop in storage over winter “so by the time you’re ready to bring it out to get ready for planting, there can be quite significant dry rot or decay on the seed.

Peters says if fusarium is really able to gain a hold on the seed and it’s then planted in cooler and wetter conditions that delay emergence, there’s even more time for the pathogens to work on the seed piece in the soil.

“Then the most serious condition is if that seed piece completely rots and you get a miss in the field. If those misses are even 10 per cent of your plants, that’s a huge yield impact,” Peters says.

“Managing fusarium at harvest and into storage can be a huge help with developing clean seed for use at planting,” he adds. “If you start off with a good seed source that’s clean from some of these pathogens, you really get yourself started on the right foot.

Potato Physiology

In addition to disease considerations, there are also physical and physiological aspects to potato seed quality. Hawkins notes physical condition (freedom from bruising and other defects) is obviously significant, but so is physiology.

“The physiological quality aspect is very important,” he says. “Unlike other crops, potatoes are vegetatively propagated. You don’t plant a true seed like you would with corn, so that pulls in all kinds of unique challenges with potatoes versus other large-scale crops, because what’s in the seed typically gets transferred to the crop in terms of health.”

Mikitzel says the physiological aspect of quality refers to a seed potato’s age and its condition.

“Physiological condition refers to primarily age. The age of a seed potato is determined by chronological age, like how many months it’s been in storage, but also by its physiological condition,” she says.

“If you have a potato that’s been in storage for six months in a very hot and stressful environment, it will have aged more than a potato that’s been in storage for six months in a very cool, non-stressful environment.”

Mikitzel says seed lots need to be stored in relatively cool conditions to keep them physiologically young, “so that when the grower gets the seed they can manipulate it how they want to and get the age that they want.”

Paget maintains knowing the age of a particular seed lot is definitely useful. “The reason why it’s good is if I know that seed is physiologically old before I get it, I’m not going to warm that seed and let it sprout once. I’m going to try to keep it as physiologically young as I can once I get it,” he says. “If that’s old seed, you don’t want to put in cold, wet ground, because it might not survive.”

Hawkins says making sure seed potatoes are physiologically ready to grow is “an important and very complicated aspect of planting the crop. You don’t want them to be over-sprouting; you want the sprouts to be ready to just initiate so the plants will emerge from the seed quickly as opposed to waiting a long time to do so in the spring after they’re planted.”

Mikitzel acknowledges that determining a seed potato’s physiological age isn’t that easy.

“The only way we can determine it now is by doing a sprouting test,” she says. “We take a seed sample sometimes towards the end of March when we know that dormancy has broken and we store them in the dark at about room temperature with high relative humidity and watch the sprouting pattern.

“If after two or three weeks you’ve got sprouts developing simply from the apical end of the potato, you know it’s a young seed lot. If you get sprouts developing from eyes from around two-thirds of the potato, we know it’s an older seed lot.”

According to Mikitzel, knowing how old a seed lot is can help determine the best way to handle it.

“If it’s young, we know that we have to warm it before we plant it to age it a little bit more to help to speed up its emergence. And if its an older seed lot, we know we have to maintain it a little cooler before we plant it, so as to not age it any more than it’s already aged,” she says.

“Growers are aware that physiological age is important but it’s something that we’d like to increase the awareness of so they can optimize the crop that they put in the ground,” Mikitzel says. “The best scenario would be for the seed buyer to get his seed early enough in the season so he could do this test on his own farm before he plants.”

Hawkins says ideally, growers should strive to match a seed lot’s age with the length of the growing season.

“Matching the right physiological age of seed with where it’s going to produced is important to maximize not only the yield but the quality of the output,” he says. “Generally, you want physiologically young seed for a long season area and you want physiologically slightly older seed for planting your crop in a shorter season area.”

 

Seed planting underway at Sean Paget’s potato farm in Simonds, N.B. Photo: Natalie Paget. Photo: Hartfelt Images by Natalie.

Seed planting underway at Shawn Paget’s potato farm in Simonds, N.B. Photo: Hartfelt Images by Natalie.

Maintaining Quality

The experts agree that ensuring proper ventilation, humidification and temperature settings in a storage facility will not only help keep seed potatoes in good physiological condition, it will prevent or reduce disease in the pile. That’s particularly true when it comes to bacteria.

“We don’t have really any treatments to manage bacteria like we do for fungi, so the key for bacteria is really about controlling the conditions,” Peters says. Bacteria love moisture and they love warmth, he adds, so anything that can be done to keep things cool and dry will reduce the chances of bacterial soft rot creeping into the pile.

Once the seed is delivered to producers, what can they do to ensure good-quality seed is put in the ground? Mikitzel, for one, believes it starts with having a good relationship with their seed suppliers.

“They can talk to their seed grower and see how they produced that crop and how they stored it,” she says. “Growers can inspect the seed when they get it, and refuse to accept a load that has an unacceptable amount of disease or is shrivelled or has excessive sprouting on it.”

Peters stresses that disease-free seed ups the prospects for a good potato crop. “Having clean seed is a huge factor. If you start off with a good seed source that’s clean from some of these pathogens, you really get yourself started on the right foot,” he says.

Paget maintains it’s essential to “use the best management practices you can to keep that seed as healthy as possible before it goes into the ground.” This includes checking that seed lots are healthy and making sure the seed doesn’t dry out prior to planting. “If you need to put humidification on seed, you do it,” he says.

Proper seed piece sizing and suberization are also important for maintaining quality, Paget notes. Hawkins agrees, stating it’s important for seed pieces to be appropriately sized depending on the variety producers are growing.

“Some varieties need to have bigger seed pieces because they naturally have fewer buds on the tubers, fewer eyes that are going to produce the stem,” he says. “So getting that right and having the proper adjustment of the seed cutter are critical to [the success of] the crop.”

Mikitzel recommends that seed pieces should be cut from mother tubers no larger than eight ounces, particularly for varieties that that have relatively few eyes or poor eye distribution on the tubers.

“We like to have seed tubers anywhere from four to eight ounces so that you can cut them in half or cut them twice and end up with four seed pieces. Then you’re pretty much guaranteed to have an eye in each one of those,” she says.

Proper Handling

The experts share the view that proper handling is primary prerequisite for maintaining seed quality.

If you handle it roughly you get bruises, and bruises take energy away from the seed piece and therefore it’s not as healthy when you go to plant it,” says Mikitzel.

“You want to make sure to minimize any drops that you subject those seed pieces to. A potato is just as susceptible to a bruise as an apple so if you drop it more than six inches you’re going to get a bruise.”

Hawkins agrees: “The way that you handle them will affect their quality in terms of damage impacts, since bruising effects the ultimate performance of the seed in the crop and what it can produce.”

He notes that bruises also serve as entry points for disease infection, adding it’s important to keep cutting implements clean and sharp to avoid tearing seed pieces, which can lead to more surface area for dehydration and for disease entry.

“The sharper the blade the better,” says Mikitzel. “If you have a sharp knife, it makes a very smooth cut; there are no ragged edges on that seed piece. Ragged edges heal very slowly if at all, and there’s more chance of disease getting in if your seed knives are not sharp. And if you don’t disinfect them regularly, there’s a greater chance of spreading disease from one tuber throughout the whole seed lot.”

Peters says seed cutting essential creates wounds that open tubers up to invasion by a number of pathogens, so disinfecting knives periodically will help prevent spores spreading to healthy seed.

Peters says non-chemical measures such as crop rotations and using green manures can help growers fight soil-borne diseases like fusarium. He adds there’s a number of seed treatments available to control fusarium in-season, but the last four or five years have seen a rapid expansion of fungicide resistance across the country.

“Fortunately in the past couple of years we’ve had a couple of new products which are liquid seed treatments registered in Canada [which] contain new chemistries,” Peters says. One of them is difenaconazole, which so far growers haven’t seen any resistance to.

“These new products really help bridge that gap of fungicide resistance,” notes Peters. “Growers who have problems with [resistance] to the older chemistries now have some new tools that can manage some of these resistant strains, so that’s been encouraging.

“Of course we have to make sure we use resistance management strategies now to keep some of these newer products in the system as long as possible before resistance develops again to some of these newer chemistries,” he says. “As soon as that happens, it can happen quite quickly.”

Peters says rotating products or using combinations of products is essential to maintaining the efficacy of new chemistries. “Mixing up the game is really important,” he says.

This seed improvement trial illustrates the effects of seed warming. Russet Burbank potatoes from the same seed lot were planted in two rows — the ones on the left were stored warm and exhibit even emergence; the ones on the right were stored cold and exhibit uneven emergence. Photo: Loretta Mikitzel, N.B. Dept. of Agriculture.

This seed improvement trial illustrates the effects of seed warming. Russet Burbank potatoes from the same seed lot were planted in two rows — the ones on the left were stored warm and exhibit even emergence; the ones on the right were stored cold and exhibit uneven emergence. Photo: Loretta Mikitzel, N.B. Dept. of Agriculture.

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