Guava (Psidium guajava L.) is one of the most economically important plant species in the Myrtaceae family. This species was described by Linnaeus in 1753 based on collections from Asia, but many botanists consider the species to be native to tropical America, with subsequent introductions to many other tropical and subtropical regions throughout the world over the past 400 years.

Guava has been designated as “the apple of the tropics” or “poor man’s fruit” because it thrives on a variety of soils, propagates easily and bears fruit relatively quickly. Food and Agriculture Organization (FAO) of the United Nations reported that the average annual production of guava is ca. 6.8 million tons since 2017. Its commercial success may result from the facts that it is cheap to grow and purchase and is an extremely rich source of vitamin C and dietary fibers and various other nutrients. Guava fruits produce six-fold more ascorbic acid than strawberry and five-fold more than kiwifruit or orange, and they are important natural sources of vitamin C. Nevertheless, the genetic basis for ascorbic acid and other bioactive compounds in guava have rarely been studied due to the absence of reference genome sequences.

Fruits of many Myrtaceae plants are woody-capsular (e.g. eucalypts), but guava fruits are soft and fleshy. This makes guava an ideal system to study fruit softening mechanisms and the evolution of fruit types. However, genetic mechanisms of fruit softening and lignification have not been well studied.

Researchers from South China Botanical Garden of the Chinese Academy of Sciences have assembled the first genome sequences of guava. This guava genome assembly is chromosome-level and of high quality. The researchers used genes co-expression network methods to study the fruit development of guava. They demonstrated that L-galactose pathway plays a major role in vitamin C biosynthesis in guava fruit. Moreover, the softening of guava fruits may result from both starch and cell wall degradation. In addition, they compared genomic information for representative plants of Myrtaceae, and found that lignin biosynthesis genes were positively selected in woody-capsular-fruited plants, and starch biosynthesis and degradation genes were positively selected in fleshy-fruited species.

"These results identified genetic mechanisms of vitamin C accumulation and fruit softening in guava. Overall, these will provide a foundation resource to support molecular breeding of guava. This study also represents a new insight into the evolution of soft, fleshy fruits in Myrtaceae." said Prof. KANG Ming, corresponding author of the study.

This study, entitled “A chromosome-level genome assembly provides insights into ascorbic acid accumulation and fruit softening in guava (Psidium guajava)”, has been published in Plant Biotechnology Journal. For further reading, please refer to: https://doi.org/10.1111/pbi.13498.