Influence of Pre-harvest Calcium and Potassium Sprays Combined with Coloured Polythene Bagging on Postharvest Quality and Shelf Life of Rainy Season Guava (Psidium guajava L.) cv. Lucknow-49

In the humid, steamy months of the rainy season, the guava tree faces a difficult challenge. While the fruit is a nutritional powerhouse, packed with vitamins and fiber, the very weather that helps it grow also works against its quality. High heat and moisture act like a fast-forward button for ripening, causing the fruit to soften quickly, lose its weight through evaporation, and spoil before it can reach a market or a family table. For farmers, this means a significant portion of their harvest is lost to decay, leaving them with less income and consumers with a product that lacks the firm texture and bright flavor they expect. To solve this, scientists look to two natural levers: nutrition and protection. Just as a balanced diet strengthens a human body, specific nutrients like calcium and potassium can fortify a fruit's internal structure, helping it hold its shape and resist the rush of aging. Simultaneously, shielding the fruit from the elements can create a calmer, more stable environment for it to mature. The question researchers ask is whether combining these two strategies—feeding the tree the right minerals and wrapping the fruit in a protective layer—can turn a fragile rainy-season harvest into a durable, high-quality crop.

A team of researchers in India set out to test this exact combination on the Lucknow-49 variety of guava, a popular cultivar grown in the subtropical regions of the country. They worked over two consecutive rainy seasons, from 2015 to 2017, in an orchard managed with standard care. Their goal was to see if spraying the trees with solutions of calcium chloride and potassium sulphate, and then covering the developing fruits with colored plastic bags, could improve the fruit's quality and how long it lasted after being picked. The scientists designed a careful experiment with sixteen different approaches. Some trees received no treatment at all, serving as a baseline. Others were sprayed with just calcium, just potassium, or a mix of both. A third group of trees received the nutrient sprays combined with bags of different colors—red, green, yellow, and blue—placed over the fruit thirty days before harvest. These bags were perforated to allow air to circulate while still protecting the fruit from insects, dust, and direct rain.

When the fruits were finally harvested and brought into the laboratory, the researchers began a ten-day observation period under normal room conditions, checking the fruit every few days. They measured how much weight the fruit lost, how firm it remained when pressed, and how the chemical makeup changed as the fruit ripened. They looked at the sugar content, the acidity, and the levels of vitamin C, which is a key nutrient in guava. They also asked a panel of judges to taste the fruit and rate its color, texture, and overall flavor on a simple scale. The results showed a clear winner among the many combinations tested. The fruits that received both the calcium and potassium spray and were covered in blue bags performed significantly better than all the others.

This specific treatment, the combination of the nutrient spray and the blue bag, kept the fruit firmer for longer and slowed down the loss of weight. While the untreated fruits began to shrivel and soften noticeably, the treated ones held their structure, retaining a crispness that is often lost in the humid season. The chemical analysis revealed that these fruits also maintained higher levels of sweetness and vitamin C. The total sugar content in the best-treated fruits reached levels as high as 17.44 percent in one year and 16.91 percent in the next, while the vitamin C content stayed robust at nearly 197 milligrams per 100 grams of fruit pulp. In contrast, the untreated fruits saw their vitamin C drop sharply and their sugar levels fluctuate less favorably. The acidity, which gives the fruit its tangy kick, also declined more slowly in the treated fruits, suggesting that the ripening process was happening at a more controlled, gentle pace rather than a frantic rush.

The blue bags seemed to play a unique role in this success. While other colors offered some protection, the blue bags, when paired with the nutrient sprays, created the most favorable microenvironment for the fruit. This combination resulted in a shelf life that was extended by eight to ten days compared to the untreated fruit. For a farmer or a seller, this extra time is crucial; it means the fruit can be transported further and sold for longer without turning to mush. The judges who tasted the fruit confirmed these scientific measurements, giving the blue-bagged, nutrient-sprayed fruits the highest scores for taste, texture, and overall appeal. They found the fruit to be more flavorful and pleasant to eat than the control group, which had become soft and less distinct in flavor.

The study concludes that this method is a practical and effective way to improve rainy-season guavas. By feeding the trees calcium and potassium and shielding the fruit with blue bags, growers can significantly reduce the waste caused by rapid spoilage. The research does not suggest that this is a magic solution that eliminates all problems, but it does show that a simple, low-cost intervention can make a substantial difference. The findings offer a clear path forward for farmers in similar climates who struggle with the quality of their wet-season harvests. Instead of accepting the rapid decline of their crop, they can use these specific sprays and bags to keep their guavas firm, sweet, and nutritious for nearly a week longer, ensuring that more of the harvest reaches the table in its best possible condition.