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Spain: Thicker-skinned oranges to prevent crackingNot so many years ago, a thin skin was one of the main qualities that defined a good quality orange; however, this concept has now been almost totally abandoned, as nobody is imposing it any more and facts point in the opposite direction, since one of the main problems is that many oranges suffer cracking while on the tree and having a thin skin makes it easier for the fruit to become spoiled. With a thick skin, it has a better chance to resist.
Carlos Mesejo, professor at the School of Agronomic Engineering and researcher at the Agroforestry Institute of the Polytechnic University of Valencia, has defined the issue of cracking of oranges as "a multifunctional problem in which various, difficult to control factors play a role." Some varieties, for instance, may have genetic tendencies, although the truth is that the issue doesn't always appear in the same way. It depends on the year.
In a conference at the Citrus Congress of Picassent, Professor Mesejo spoke about the main physiopathies suffered by citrus fruits and focused especially on the issue of cracking, as it is becoming a bigger problem. "In many cases, it has been reaching worrying levels this year," acknowledged the researcher.
Physiopathies are plant diseases which do not have a biotic origin. In other words, they are not caused by microorganisms (viruses, bacteria, fungi...), but are due to imbalances motivated by physical or environmental reasons (climatology, soil...) more or less accentuated by the genetic tendencies of each species or variety.
Citrus growers suspect that one of the main factors behind this problem is the varietal patters used, for which there is no alternative, because these are tolerant to the Tristeza disease, and if it wasn't for them, there would have been no citrus industry for years.
Carlos Mesejo explained that the characteristic that ultimately determines if an orange will crack and burst is its water absorption capacity at certain stages of its growth and the lack of elasticity of the skin to resist such a stretch.
He denied that the use of treatments with gibberellic acid (suitable nevertheless against the claret) could interrupt the problem and said that, on the contrary, it could intensify it. Moreover, he recommended treatments aimed at "increasing the thickness of the skin," with applications between June and July of solutions based on calcium nitrate.
The researcher of the Polytechnic University outlined the circumstances in which excessive water absorption will cause the fruit to burst. He said that one factor that can have an impact is the rainfall recorded between August and September, even small rainfall of just a few litres per square metre, and concluded that "more rain results in more cracking."
Important for insurers
This conclusion is of great importance, because Agroseguro has been arguing that harvest losses caused by cracking shouldn't be covered by their insurance, saying that the issue is not derived from meteorological incidents, but from deficiencies in the crop (thus blaming the producer for it), and it has sometimes cited technical reports that would back this idea.
But this new technical report, outlined in public, reveals that the cracking of oranges is potentially related to many factors, but in the end, what causes the fruit to burst is rainfall being recorded at certain times (end of summer-early autumn), and especially if they follow months of environmental drought. It is not a matter of irrigating more or less. This can be done perfectly, without deficiencies, and cracking will still occur.
Mesejo also said that this problem is more pronounced in sandy soils, because in case of sudden rainfall, the water can put more "pressure" on it. In any case, he stressed that the only real way for growers to tackle this difficult problem is by trying to grow oranges with a thicker skin.
Publication date: 11/8/2017
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