Plant Gene and Trait 2025, Vol.16, No.1, 1-14 http://genbreedpublisher.com/index.php/pgt 6 In recent years, MD-2 has become the most mainstream pineapple variety in the global market. This variety was bred and promoted by Del Monte, and its current planting area has exceeded that of all other varieties. Yow et al. (2021) pointed out that compared with the traditional Smooth Cayenne, MD-2 fruits are sweeter, have a longer shelf life after harvest, and perform better in dealing with common problems such as browning of the core. Genetic studies further show that MD-2 has unexpected genetic diversity and complex genetic structure, which is an important reason for its high adaptability and wide market acceptance. The success of MD-2 not only reflects the application effect of modern molecular breeding technology in actual production, but also reflects the results of comprehensive consideration of fruit quality, storage and transportation performance and planting stability in commercial breeding. There are also several regionally dominant varieties in Southeast Asia, Africa, and Latin America, such as Queen, which has smaller fruits but rich flavor and is mainly used for fresh consumption. Red Spanish has strong disease resistance and good transportability, and is favored by growers in the Caribbean. Pernambuco has soft, sweet flesh with low acidity and is very popular in the Brazilian market (Ali et al., 2020). 4.2 Germplasm contributions to modern varieties Modern pineapple breeding relies heavily on germplasm resources from different regions. Traditional local varieties and wild relatives provide a crucial genetic basis for the improvement of existing commercial varieties. Zhou et al. (2015) found that wild types such as Ananas comosus variant A. bracteatus and A. ananassoides have passed on some valuable traits to modern cultivated varieties. These wild relatives enrich the genetic diversity of cultivated varieties, especially in terms of resistance to fungal, bacterial and viral diseases, providing key traits that were originally scarce in commercial varieties. With the help of genetic tools such as SNP molecular markers, researchers can also trace the source of specific traits. These markers reveal the genetic composition of different pineapple strains and greatly improve the accuracy and targeting of breeding work. For example, the whole genome map of the MD-2 variety released by Yow et al. (2021) has become one of the core reference resources for current pineapple research. The map clearly marks the gene regions associated with important traits, providing guidance for breeders, so that future pineapple breeding can be promoted more systematically and efficiently. 4.3 Genetic bottlenecks and breeding limitations One big problem in the pineapple industry today is that people rely too much on just a few kinds of pineapples. This has caused what scientists call a “genetic bottleneck”, meaning there isn’t much genetic difference between the plants (Zhou et al., 2015). Varieties like Smooth Cayenne and MD-2 are grown almost everywhere, so the genetic makeup of pineapple crops is very limited (Zhang and Ming, 2018; Valentino et al., 2023). Because of this, pineapples have a harder time dealing with new diseases or changes in the environment. They don’t have enough natural variety to stay strong in the face of problems (Chen et al., 2017). Breeding pineapples is also hard. They don’t pollinate themselves and are mostly grown from parts of the plant like suckers or runners. This means it takes a long time to create new types. Each new variety needs to go through many rounds of testing and selection, which is a long and tiring process. Scientists are actively exploring how to increase genetic diversity through sexual reproduction and using molecular tools to study key gene families. For example, the ATP-binding cassette transporter (ABC) gene family has been shown in recent years to be closely related to plant stress response and disease resistance mechanisms (Chen et al., 2017). 5 The Role of Germplasm Exchange in Pineapple Breeding 5.1 Hybrid breeding and hybridization strategy Pineapple breeding mainly relies on hybridization and genetic recombination to combine the excellent characteristics of different varieties to cultivate new varieties with high yield, high quality and strong stress
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