Marketable yield is more important than total yield. Physiological disorders like ‘blotchy ripening’ typically do not affect total yield but do reduce marketable yield, which reduces income and profit potential.
Description
Blotchy ripening refers to one or more conditions specific to the external and/or internal color of tomato fruit. Ideally, the skin and flesh color of mature tomato fruit are uniform throughout, with red being most common. Fruit
exhibiting blotchy ripening have discolored sections. For example, defected fruits are mostly red on the outside but contain areas that are green, yellow, gray, or paler red than the remainder of the fruit, such as shown in the picture. Blemished areas may be more common on the half of the fruit nearest the stem. The flesh, especially vasculature, of fruit exhibiting blotchy ripening may be brown or broken down.
Symptoms associated with blotchy ripening have underlying physiological, or disease or insect feeding causes. Symptoms can be mild and in only a small number of fruit or severe and/or in many fruit. Regardless, it is important to note that fruit are said to exhibit blotchy ripening only when they are also in the mid-late stages of ripening as determined by changes in firmness and other variables and when insect (e.g., whitefly) and disease (e.g., TMV) are ruled out as causal agents. These two criteria separate truly ‘blotchy’ ripened fruit from firm, immature fruit in the early stages of ripening (which can be mottled in color inside and out) and fruit damaged by the action of pathogens and/or insects. Blotchy ripening is a physiological disorder.
Blotchy ripening has been discussed as a potentially significant marketable yield issue in research and extension publications for nearly ninety years. Seaton and Gray of the Michigan Agricultural Research Station reported on their analysis of the anatomy of blotchy-ripened fruit in 1936. Also, after touring commercial and research farms throughout the U.S., Minges and Sadik of Cornell University published a protocol for evaluating blotchy ripening in 1964 (https://journals.flvc.org/fshs/article/view/100632/96587). These landmark works provided much needed insight on blotchy ripening, and they were followed by other steps that helped identify factors that contribute to the disorder.
Contributing Factors and Prevention
1. Genetics
Immature tomato fruit are green and photosynthetic. Later however, the set of pigments found in fruit of most hybrids shifts and red becomes the dominant color.
This shift is pre-programmed but influenced by conditions surrounding the fruit and within the plant and soil. The first and one of the most reliable steps in minimizing blotchy ripening is selecting varieties known to display it very infrequently – i.e., among few crops year to year and among few fruit within a season.
Hybrid tomato varieties are the culmination of huge, coordinated efforts requiring in-depth knowledge of tomato genes. Nearly 100 years ago, these genes were found to include a natural mutation that led individual fruit to ripen uniformly red, today’s most common standard. Decades of development of varieties whose fruit turn red over their entire surface and throughout their flesh at precisely the right time relative to other variables related to market-readiness have followed. However, the natural condition of NON-uniform reddening remains in the tomato genome and it shows itself most readily in certain varieties. As a category, heirloom varieties may display the blotchy ripening disorder most consistently. As an early step in avoiding blotchy ripening, consult reliable reports on variety performance in your area and select varieties that exhibit the problem rarely, if at all.
2. Environmental Conditions, including Air Temperature, Soil Status, and Nutrient Levels
A variety’s genes may predispose it to physiological disorders like blotchy ripening but this weakness can be minimized or masked with luck and proper management. Factors contributing to the development of physiological disorders like blotchy ripening can be difficult or take a long time to determine because they are difficult to induce experimentally. That said, research and experience have shown that blotchy ripening is most prevalent when air temperatures during mid-late stages of fruit ripening are extreme (e.g., below 60 deg F and/or above 90 deg F) or highly variable, when humidity levels remain high, and/or when these conditions are common and light levels are low. Low soil quality and high salinity are also associated with the occurrence of blotchy ripening.
Most also agree that severe cases of blotchy ripening are most often associated with factors that limit the supply of potassium (especially) and to a lesser extent, magnesium, to maturing fruit. These factors include: waterlogged and/or compacted soils, below-optimal potassium or magnesium application rates, above-optimal nitrogen application rates, excessive application of potassium and magnesium competitors, excessively large or dense canopies, and the environmental conditions mentioned previously.
Potassium supplies may be restricted for different reasons. So, do not over-compensate when evaluating and adjusting irrigation and nutrient management practices. Articles written by Gordon Johnson (University of Delaware), Jerry Brust (University of Maryland), and others are excellent overviews of blotchy ripening and its management. All point to limiting blotchy ripening and similar disorders through careful nutrient and water management, considering soil, plant, and fruit factors in the process.
Limiting the Occurrence and Severity of Blotchy Ripening in Tomato
A. Select resistant varieties.
B. Minimize large temperature swings and extreme high temperatures during fruit development and ripening.
C. Ensure adequate and balanced nutrient levels, paying special attention to potassium and magnesium and their competitors or factors that limit their availability.
D. Maintain consistent and appropriate soil moisture levels.
E. Maintain or improve biological, chemical, and physical characteristics of soils allowing them to support maximum root and plant health.