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202403 Fresh Quarterly Issue 24 06 Pick Postharvest Winners Web
Issue 24March 2024

Pick postharvest winners

Growers consider many factors when deciding which cultivars to plant — postharvest performance should be one of these. By Anna Mouton.

Planting trends often follow fruit prices, observes Keith Bradley, general manager of Fruitways AgriServices. “People look at their returns on the bin when they order their trees, but a high bin price doesn’t necessarily mean a high return per hectare.”

An orchard’s gross income is driven by the number of cartons exported and the price they fetch. Fruit that succumb to postharvest disorders are fruit not sold, so high-value cultivars that suffer significant postharvest losses may be less profitable than more robust lower-value cultivars.

Bradley uses Packham’s Triumph as an example. This old pear might seem unexciting, but it’s grower-friendly and will consistently produce high yields of storable fruit.

“It’s low risk,” says Bradley. “Now, your price per kilogram for top-quality Nicoter apples would be far in excess of the top price for the best Packhams. But for most growers, the per-hectare income of Packham’s would far outstrip that of Nicoter.” Nicoter’s postharvest issues are part of the reason.

Whereas most growers are sensitive to cultivar differences in establishment and production costs, they may be less attuned to the erosive effects of postharvest disorders on profits.

“It’s simple arithmetic,” explains Dr Nigel Cook, horticultural consultant and plant breeder at Innovapome. “If you lose a third of your fruit postharvest, the remaining two-thirds must carry all the costs, so it goes up by 50%. And you can easily lose a third of your apples to bitter pit in a sensitive cultivar.”

Considering that costs incurred after harvest may outstrip production costs, Cook stresses that growers can’t afford postharvest disorders. “We need to stop planting cultivars with genetic defects like greasiness and pitting disorders.”

The bitter pit example

Bitter pit usually appears during storage, but the problem originates on the tree. Although mineral balance influences bitter pit development, genetics determine whether cultivars are susceptible. South African growers will doubtless be aware of Golden Delicious and Braeburn’s tendency to bitter pit.

Braeburn is one of the parents of Nicoter — better known by its trade name Kanzi — which is likewise prone to pitting disorders.

“Nicoter looked very attractive as a new cultivar,” recalls Bradley. “There was a demand for it, and it fetched a high price. So, people planted a fair number of hectares.”

According to Bradley, growers were able to grow the trees, but attaining the required colour specification was challenging, and then the fruit manifested bitter pit and lenticel disorders during storage. “At the end of the day, although the cartons that made it to Europe attained excellent returns, there were just not enough cartons per hectare.”

In the case of Golden Delicious, Bradley remembers a time when high bitter pit losses led to questions about its viability in South Africa. “But through collaboration between the industry research bodies, people worked through it, so that Goldens are now widely grown successfully because bitter pit has been brought to acceptable levels.”

Links to genes

“Traits are usually linked because of their position on the chromosomes,” notes Cook. “The closer traits are on a chromosome, the more closely they are linked.”

When selecting desirable traits like colour or yield, the risk is that a breeder inadvertently also selects for undesirable traits like pitting disorders. Traits that show up early are easier to eliminate than ones that suddenly appear when the first shipment lands in Europe.

“As a breeder, if I see bitter pit on a tree, I cull the tree,” says Cook. “You don’t want to plant something with a defect. It’s not worth it.”

Fortunately, as he explains, apples are polygenic for most traits. They have many different genes that influence their traits. This makes apples complicated, but it means breeders can access multiple genetic options to achieve a specific outcome.

One example is the development of low-chill apple cultivars. Many currently available low-chill apples have a reputation for poor storability, which is related to their selection from early flowering trees with short fruit-development periods.

“Early flowering and short fruit-development periods seem to go together,” says Cook. “And these trees tend to have lower chilling requirements.”

He speculates that early-ripening low-chill apples probably have high respiration rates, as this is generally true for early-ripening fruit of any species. High respiration rates lead to a shorter postharvest life — a classic case of living fast and dying young.

In his own breeding programme, Cook has selected low-chill apples that ripen later in the season, thereby avoiding selection for unwanted postharvest problems.

Putting the puzzle together

Bradley and the Fruitways team, including pack-house and postharvest-quality representatives, meet every year to discuss planting recommendations for the growers in their group. They consider aspects such as how easy the tree is to grow, the harvest window, storability, and marketability.

“We build all that into a model,” says Bradley. We look at the total plantings within our group. Then, we can say which strains of which cultivars we back and which ones growers should maintain but not expand.”

When faced with entirely new cultivars, Fruitways plants a few sample trees in their trial blocks in Elgin and Vyeboom. Besides assessing tree phenology and growth, they also submit fruit to their postharvest-quality specialist at the pack house.

“A cultivar needs to store a minimum of 42 days,” says Bradley. “We do 42-day assessments, as well as taking it to 6–8 months, to see what the storage potential is.”

The initial trials take several years. If a cultivar shows promise, Fruitways will establish 150–300 trees for more extensive trials. This gives them enough fruit to fill multiple bins and test different storage regimes under commercial conditions. If the fruit hold their own, the marketers are brought in.

“Once we’re comfortable, we’ll approach our growers,” says Bradley. There’s still risk because it’s at an early stage, but we think the cultivar has upside potential.”

In the past, new cultivars were often planted based on their performance in other parts of the world. “The cost of establishing a hectare and running it for several years, and then having problems, is high,” comments Bradley. “A hectare costs a lot of money, especially when it fails.”

Cook agrees. “If you’re going to get into the business of growing apples, you better make sure you’re growing quality apples. Otherwise, the value chain will eat you up — it’s just too expensive.

“But if South Africans grow a good apple and deliver it in good condition, we will earn good money.”

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