By: Héctor García O., Co-Founder and General Manager of Diagnofruit Laboratories Ltda, SOCHIFIT Member [email protected]
Very early in the season, after catastrophic rains in the central part of the country and with a very unstable spring, we could predict that this would be a very complex year in terms of production and phytosanitary. All the adverse climatic scenarios that we could have predicted have occurred or are developing: Spring rains, very unstable initial general behavioral framework, post-setting rains, with early ripening cherries, and the finish with “abusive” heat waves They mark a very complex season, with much development still, for which we must be prepared, since the conditions for Botrytis, and other characters in his gang, are very present and could cause losses due to rot, not only in cherries, but also in other species such as blueberries, grapes and kiwis.
In several talks and training sessions given since the end of winter and the beginning of the season to post-harvest teams, I mentioned that this year I would not like to be in their shoes, since it would be a season full of stress and extremely challenging; it was not very difficult to make a mistake in that diagnosis, but the idea was to establish a level of concern that would keep us alert. (see previous article)) which in many cases, due to the strangeness of the season, I feel I have fallen short in predictions.
For cherries, the worst scenario when we talk about rots is that it rains during the period of fruit development, when it is already reaching maturity, since the cracks are the entry point for more than one species of phytopathogenic fungus; for other species, such as grapes, kiwis, blueberries, in addition to the period of growth and maturity, the flowering stage is added as an important component when it comes to generating rots at harvest and post-harvest, since the inoculum remains installed waiting for conditions that allow its development. This spring, both conditions were possible; flower infections were higher than in recent years and the appearance of rots in cherries has been a headache that we have not yet overcome despite being in a warm and dry period.
In early spring, when analyzing the flower monitoring carried out on cherry blossoms, although we did not observe much activity of Botrytis and Alternaria, the amount of Pseudomonas It gave us the first immediate control alert, but at the same time, another medium-term alert appeared, another of the gang that we had lost in recent years appeared, Geotrichum, which causes acid rot in cherry and other stone fruits (Fig. 1).
Beyond the inoculum, another characteristic that marks this season and creates a problem for efficient control is the degree of phenological heterogeneity (perhaps not the most technical name, but the most illustrative), which presented us with several states in the same cherry tree. By having a phenological mix, applications that are intended for flowers do not have the same effect as for a formed fruit or vice versa, and that can result in loss of control. At the same time, management that make susceptible The risk of rotting fruit, such as certain growth regulators, increases because part of the fruit on a tree is not at the most harmless time to avoid certain negative effects; this has been well known and was a warning that we repeatedly made to technicians, but it is very difficult to control.
In other species such as table grapes, although only part of the flowering occurred during significant rainfall, the development of the process was very slow, which left windows in some cases, decreasing the effectiveness of control programs. As exploratory data, in the last 3 years in grape flowers it was very difficult to detect frequencies of colonization by Botrytis of more than 5%, this season it is more difficult to find orchards below that value and there are quite a few that reach 20% and more. In wine grapes, where control programs are less aggressive, we have detected cases of attacks by Botrytis leaf and cluster growth in early stages of development (Fig. 2).
One last aspect to consider is the quality of the fruit. In general, hesitant springs do not produce good quality, which is what a standard for fruit produced in Chile requires, with long journeys and demanding markets. At the beginning of spring, we insisted a lot on the possibility of mobilizing calcium to the fruit, which very often did not happen, especially in early varieties. Beyond being a factor of susceptibility to rot, the imbalance also results in less firm fruit, with more pitting, bruising and, apparently, browning in cultivars susceptible to this disorder; all characteristics that we have observed to a greater or lesser extent in 2023-24 and that we must continue to monitor.
What types of rot do we see most frequently this season?
As we mentioned, certain pathogens had disappeared from our radar because the dry conditions of recent years did not allow them to develop properly; they were rather isolated cases. However, and considering everything described, this season certain enemies have returned with great force and we must confront them.
Since the beginning of the season, grey rot has been the disease most frequently detected from samples taken from packing plants (Fig. 3), where the development of the symptom is very early and often confusing, so it is always necessary to carry out humid chambers to confirm the presence of the different pathogens. At the same time, although the quantity is generally low according to qPCR analysis, it is easier to detect contaminations of Botrytis cinerea in cherry packing line wells. In previous years, detections occurred at the beginning of the season and then at the end with fruit from the south; this campaign, its detection has been extended over time, even in week 52, a phenomenon that had not occurred in the last 3 years.
Alternaria and Cladosporium, although they are frequent, have given way to the development of other pathogens with greater intensity. Both infections have something positive for us, and that is that in post-harvest the contagion is very reduced from fruit to fruit.
Geotrichum and other yeast-like organisms, this is a critical point to consider that adds to Botrytis and they are agents that easily cause contagion during the trip. Currently, Diagnofruit monitors cherry process water (hydrocooler or lines) from at least 40 cherry packing plants, considering the largest exporters in the country, so probably more than 70% of the national production is being controlled with the quantification service through qPCR-Taqman multiplex; a large part of this is done thanks to an agreement with PACE Int-Sumitomo. We have scaled up the technique, which was started with the help of CORFO in 2016 and this season we have reports between 24 -48 hrs post sampling, which generates a quick response option in the packing when we observe contamination problems, promoting increases in sanitizer concentrations, reduction in the number of hours of water use, etc.
Previous seasons, Geotrichum In 99% cases it was below the detection threshold of the technique; however, this year the reality is very different, at least 20% of the samples show some level of this yeast in the water, and in some cases reaching very close to critical levels.
As we pointed out, in the orchards, we already detected the fungus early on in flowers and small fruits (Fig. 1), so we expected development in the harvest. In particular Geotrichum It is very difficult to control, triazoles are the only synthetic fungicide option and, although we have intensified their use this year, the effectiveness is not as high, because the fungus easily exhibits resistance, due to the selection pressure exerted by the only widely used molecule, which is tebuconazole.
Other yeasts are detected causing rot or at least are present in fruits with signs of acid rot, the problem is that we do not know the epidemiology; particularly, this year we saw attacks on early fruit with cracks, which sheds light on how the infectious process could start. These microorganisms are present on the surface of leaves and fruits, they are generally not pathogenic, but certain conditions that we do not know allow them to advance to the harmful level of phytopathogens. Water is easily contaminated with these fungi (Fig. 4), however, their presence will not necessarily result in infections of healthy fruit, but it is an alarm to keep our systems as clean as possible, with sanitizers at the highest possible levels of use.
In conclusion, we still have a long way to go, the most problematic fruit has already been packed, but there are still inoculum remnants with susceptible fruit, do not neglect field or post-harvest applications (ensure residues, see previous article), eventually reinforce programs with fungicides based on botanical extracts and/or Bacillus as a general strategy, in addition to maintaining or adding Botryticides close to harvest, which have in their formulation fungicides of the phenylpyrrole, hydroxyanilide or carboxamide groups, also considering the use of tebuconazole to protect us from Geotrichum, always respecting deficiencies according to national regulations and sales strategy.
