Mango Breeding

M. indica is the most important species of the genus, as a producer of the most delicious tropical fruit, the mango. It The mango (Mangifera indica L.) originated in north- is closely related to M. longipes Griff. and M. sylvatica eastern India, the Indo-Myanmar border region, and in Roxb. Bangladesh, where it is still found as a wild tree bearing very small fruits. It is also known to occur in the lower Mango (Mangifera indica L.) is the most important Himalayan tract, near Nepal, Bhutan and Sikkim. As per fruit crop in India with considerable socio-economic Mukherjee (1953), mango has been cultivated for the past significance. It is known as the ‘King of fruits’ owing to 4000 years at least, with over 1000 varieties under cultivation the delicious quality of the fruit rich in vitamins and during this time. minerals. Its long period of domestication is evident from its mention in the ancient Indian scriptures. Ancient Indians The genus Mangifera belongs to the order Sapindales valued mango not merely for the sentiment or religious in the family Anacardiaceae. consideration, but also they realized its importance in the Detailed classification is as follows: economic and cultural life of their society. Mughal kings promoted the practice of planting the best varieties: Lakhi Division : Magnoliophyta Bagh (one lakh tree) planted by Akbar the Great is well- Class : Magnoliopsida known in history. Ain-I-Akbari, an encyclopedia written Sub-Class : Rosidae in 1590 AD gives an ample understanding of mango in that Order : Sapindales period. However, research with specific objectives started Family : Anacardiaceae by the turn of the last Century. Mango is rich in Vit A, C, Genus : Mangifera flavonoids, carotenes, glucosides, sterols, terpenes, aromatic The five species, M. sylvatica, M. khasiana, M. acids, essential oils, fatty acids and phenolics. It is a _andamanica, M. indica and M. camptosperma reported to_ powerfully nutritive fruit, containing most of the essential be found in India, are distinctly different from each other. substances needed by the human body.

Bompard (1993) listed more than 60 species worldwide, with the highest diversity found in the heart of the distribution area of the genus Mangifera, i.e., the Malayan Peninsula, Borneo and Sumatra. In India, more than one thousand varieties are grown (Mukherjee, 1953), all of which belong to Mangifera indica L. Field gene-bank collections made in the country, to a very great extent, represent this vast gene pool. The vast diversity in indigenous mango varieties, mainly of seedling origin, has remained unexplored. However, there are still regions within the country that have not been explored for mango wealth. This unexplored genetic diversity can be a source of very important traits. It is possible that desirable traits like disease or pest resistance are available in this gene pool. It is in this context that the concepts of ‘On-farm conservation’ and ‘Custodians of genetic diversity’ assume great importance. The UNEP-GEF TFT project successfully identified 54 farmers who were conserving genetic diversity in their own orchards for various purposes, viz., better pollination, to regularity of bearing, to fruits to be used for different purposes. One example is identification of some seedlingtypes in Chittoor, wherein varieties with a high carotenoid content and excellent shelf-life were noticed (Dinesh et al, 2015). Hence, not withstanding problems of nomenclature ambiguity there is a scope for locating genotypes with desirable traits by germplasm surveys, evaluation and characterization. Chances for improvement from germplasm survey in the heterozygous perennial mango are definitely higher than that through hybridization programmes, in our experience. Hence, if the vast diversity is adequately assessed and utilized, it can be a boon for improvement.

The large gene-pool in mango needs to be conserved. In situ conservation, so far, has not been able to prevent genetic erosion due to several factors. Ex situ conservation has the limitation of a variety not expressing itself fully due to the environmental effect. This also needs a large area, which is a difficult proposition. Hence, the concept of ‘Core collection’ needs to be adopted. However, for a heterozygous population, it is to be seen very critically whether a suitable representative sample can be selected. Under these circumstances, ‘On-farm conservation’ is one of the strategies that can be satisfactorily adopted. Dinesh et al (2015) observed that several of the seedling-types being grown as heirloom varieties, are conserved in farmers’ orchards. Andhra Pradesh is home to many juicy type of mangoes known as ‘Rasalu’ types, viz., Chinnarasam, Peddarasam, Cherukurasam, etc. Registration of these varieties with PPV&FRA can result in conservation and, further, the farmer can also receive royalty for his sustained effort.

The genetic base of polyembryonic varieties in mango is very narrow, unlike in monoembryonic varieties. Major mango producing countries, viz., Australia, Philippines, etc. have polyembryonic types as a commercial variety. Polyembryonic types, in India, are mainly located in Western Ghats, in the coastal and North-eastern regions of the country. Due to their propagation by nucellar seedlings, no large diversity is noticed in these types. Polyembryony in mango is genetically controlled. Leroy (1947) opined that the presence of one or more recessive genes results in adventive embryony. Sturrock (1968) also observed that when monoembryonic varieties were crossed with polyembryonic varieties, the resultant progenies indicated monoembryony as a dominant trait. However, Arnon et al (1998) observed that dominant genes controlled polyembryony. Brettell et al (2004) also opined that dominant genes controlled polyembryony. In addition, they concluded that this varied with location.

Some correlations worked out in mango have shown leaf flavour to be directly correlated with fruit flavour (Majumder et al, 1972; Whiley et al, 1993). Emergence of new growth flush simultaneously with fruiting, or immediately after harvest, indicates that the tree is going to be regular in bearing (Sharma et al, 1972). Higher phloem to xylem ratio was found to be associated with the dwarf stature. If this ratio exceeds 1.0, the trees tend to be least vigorous; if this value is 0.6 to 1.0, the trees will have medium vigour; those with a ratio less than 0.6 will be the most vigorous (Kurian and Iyer, 1992). Higher amount of phenolics in the apical bud has also been shown to be associated with the dwarf stature (Iyer, 1991). Majumder et al (1981) had earlier reported that lower stomatal density was an indication of dwarf stature. Pre-selection indices are pointers to selection prior to the main selection of a trait in question. These are extremely important as they save time, space and money. The concept of pre-selection index is not very new. Van Mons first reported it in 1835, and Mitschurin in 1969, based mainly on their practical experience. In mango, there is a need to look for morphological, molecular and biochemical markers. Campbell and Zill (2009), using leaf aroma, screened thousands of seedlings at their juvenile stage.

Mango, being highly heterozygous, has a large diversity that has resulted from propagation by its seeds. This, in turn, has resulted in ambiguity in nomenclature as, the same variety is known by different names in different regions. Diversity studies would help choose parents, so that heterosis can be exploited for various traits. Souza et al (2011) evaluated genetic variability of mango (Mangifera indica L.) accessions, of which 35 originated from Brazil, six from USA, and one from India. These accessions were found to have considerable genetic variability, demonstrating the importance of analyzing each genotype in a collection, to efficiently maintain a germplasm collection. Start codon targeted (SCoT) markers were used to investigate genetic diversity of 73 mango accessions in- China, and, the studies resulted in these accessions being grouped into four (A, B, C, D) clusters. This corresponded well with their geographical origin and known history, indicating its importance for germplasm characterization, improvement, management and conservation (Luo et al, 2012). Ravishankar et al (2013) evaluated genetic diversity and relationship among 269 mango (Mangifera indica L.) cultivars of the Indian peninsula using ‘Sequence Tagged Microsatellite Site (STMS)’ markers. Gao et al (2013) studied 200 accessions of mango (Mangifera) from exotic and domestic sources as test material. Their result showed that the germplasm cluster developed did not completely correlate with their geographical origin and type of embryo. Through an eco-geographic survey covering three regions of the state of Andhra Pradesh, 31 accessions of ‘Beneshan’ (BN Acc-l to BN Acc-31) were selected, and their fruit and leaf samples collected to study intra-cultivar heterogeneity, based on morphological fruit traits and microsatellite markers, respectively, by Begum et al (2012). In situ characterization and evaluation of fruit samples revealed phenotypic variation among ‘Beneshan’ accessions. Of the 109 mango-specific simple sequence repeats (SSRs) validated, 23 were polymorphic. Highly polymorphic microsatellites like SSR-80, SSR-87, SSR-28, and SSR-89 were more useful in differentiating these ‘Beneshan’ accessions. Dillon et al (2013) evaluated eleven (11) microsatellites markers for their usefulness in identifying varieties, validating progeny and parents, and to estimate genetic diversity in populations. The markers proved ideal for fingerprinting varieties, with an average of 8.36 alleles per locus, identified to distinguish all of the 105 accessions tested, used 25 EST-SSR markers to study the extent of PCR amplification, polymorphism and heterozygosity across a diverse selection of varieties of M. indica and related Mangifera spp. available at Australian National Mango Genebank (ANMG). These markers exhibited polymorphisms Xable of identifying a total of 86 alleles, with an average of 5.38 alleles per locus and distinguished all the Mangifera selections. The study has been utilized for identifying progeny and parents for selection, and, application of this extended panel will further improve and help design mango hybridization strategies for increased breeding efficiency. Thus, genotyping Mangifera accessions with microsatellite markers can quickly reveal genetic diversity among accessions. Sane et al (2015) studied genetic variability among 11 mango genotypes using inter-simple sequence repeat (ISSR) primers. Of the primers tested, di-nucleotide and tri-nucleotide repeats gave clear and reproducible band profiles. Highest similarity was observed among ‘Dwarf Rumani’ and ‘Creeping’. ‘Moreh’ and ‘Sabre’ (both being polyembryony types) grouped together in Cluster 2. The high degree of polymorphism and reliable amplification confirmed utility of DNA markers for genetic diversity studies in mango. Diversity studies and relatedness of accessions help Genetic studies carried out using over a thousand hybrid progenies by Sharma and Majumder (1989) showed that dwarf stature, regular bearing and precocity are controlled by recessive genes. Regularity in bearing appeared to be linked to precocity, and, the character contributing to biennial bearing is dominant over those governing the regular-bearing habit. Sharma (1987) opined that additive genes controlled flesh color. However, Iyer (1991) observed that light-yellow colour was dominant over orange-yellow in the progenies of Alphonso X Neelum cross. Dinesh (2003), in a study carried out using half-sib analysis, found that fruit characters like fruit weight, TSS and pulp percentage were controlled by non-additive factors, and heritability was low. Lavi et al (1998) concluded that parents should not be chosen on the basis of phenotype, since, offspring performance is quite unpredictable. As for skin colour, it was found that when red coloured varieties were crossed with green coloured varieties, gradation of colour in the progenies indicated that fruit colour was controlled by a number of loci (Sharma, 1987; Iyer & Subramanyam, 1987). Presence of a beak on the fruit seems to be dominant, as, all of the progeny had the beak on their fruits when ‘Totapuri’ was used as one of the parents (Iyer and Subramanyam, 1979). Bunch-bearing was found to be dominant over single-fruiting (Sharma et al, 1972). In open-pollinated progenies, Lavi et al (1989) observed no maternal effect on juvenile period and fertility, but there was maternal effect on harvest season and fruit colour, and a slight effect of maternal parent on fruit size and taste. Cytoplasmic inheritance was observed for resistance to bacterial canker as all the progenies were found to be susceptible when Neelum was used as the female parent, irrespective of the male parent used (Sharma and Majumder, 1989). Iyer (1991) observed that recessive genes mediated internal breakdown (spongy tissue). Sharma and Majumder (1989) found that dominant genes controlled susceptibility to mango malformation, as, crosses with ‘Bhadauran’ (a resistant variety) did not yield any resistant hybrid. 1. Upright habit of the tree as dominant over spreading, and, spreading as dominant over dwarfness.

Improvement in the hybridization technique, using a few flowers in a larger number of panicles for crossing, and then, covering the panicles with polythene bag instead of the muslin bag, resulted in raising a large number of hybrid progenies. In fact, one of the main reasons for success in later work on hybridization wa