Qualitative descriptors for both clove and bulb had low diversity, H’= 0.22 while quantitative descriptors had intermediate diversity, H’= 0.51 (Fig 1; Table 2).
Fig 1: Dendrogram of eight garlic accessions based on morphological characteristics.
Table 2: Qualitative morphological trait differences among garlic accessions (n=8).
For clove descriptors, both qualitative and quantitative traits showed intermediate diversity, H’= 0.38, except for the number of cloves per bulb, having low diversity (0.23). On the other hand, no diversity was found in all of the qualitative bulb descriptors but bulb skin color with intermediate diversity (0.34) while both the quantitative descriptors, bulb height and weight, exhibited intermediate diversity (0.65) (Fig 1; Table 3).
Table 3: Quantitative morphological trait differences among garlic accessions (n=8).
Interestingly, only the intensity of anthocyanin coloration at the pseudostem base registered high diversity, H’= 0.82, among all the qualitative descriptors while only the number of cloves per bulb recorded low diversity for quantitative descriptors. The low diversity observed for qualitative traits can be attributed to geographical relatedness as discussed previously in Egea et al., (2017)
and Kumar et al., (2018)
where accessions collected from neighboring locations tend to cluster together. Comparably, Trani et al., (2005)
observed high genetic diversity for quantitative traits among garlic germplasm in Sao Paolo, Brazil. This is, however, contrary to the findings of Panthee et al., (2006)
on the discriminating value of qualitative characters at the varietal level, as with the case of garlic accessions from greater Asia and Southeast Asia having highly similar quantitative traits for clove and bulb (Hirata et al., 2016).
This only confirms that morphological traits alone do not always readily reflect genetic variations among germplasm collections.
Cluster analysis using both qualitative and quantitative traits revealed three clusters (Fig 2).
Fig 2: Bulb structure of eight garlic genotypes (A. Mindoro; B. Ilocos White; C. Batanes White; D. Ilocos Pink; E. Mexican; F. Bang-ar; G. Ilocos Tan Bolters; H. MMSU Gem).
Mindoro White can be delineated by its light violet clove skin colour. Batanes White, Bang-ar and Ilocos Pink showed similar morphological characters having long bulb height and low intensity of anthocyanin coloration at pseudostem base. On the other hand, the rest of the accessions have relatively smaller bulbs exhibited in its bulb height and weight.
Alliin content determination
The eight garlic accessions were found to contain significantly different alliin contents (Table 4).
Table 4: HPTLC quantification of alliin content of garlic accessions.
Among these, Bang-ar and Mindoro White showed the highest, 37.70±0.70 mg/g and lowest, 17.22±0.68 mg/g, alliin contents, respectively. The observed higher alliin content in the varieties grown in areas under Type I climate (with pronounced wet and dry seasons), compared with Mindoro, cultivated within Type 3 climate (without pronounced wet and dry seasons) corroborates the findings of Singh and Hiremath (2013)
that alliin content varies among garlic varieties grown under differing climatic conditions. In addition, Huchette et al., (2005)
confirmed that along with genotype influence, environmental conditions affect alliin accumulation in garlic. According to Rahman (2007)
, alliin is the main sulfur compound in raw and powdered garlic, averaging ~8 mg/g alliin per clove, with the highest attainable content of 20-25 mg/g in powder form. The alliin content of Philippine garlic varieties is comparable with those of the Indian garlics and higher than those from China (Siddiqui et al., 2016)
and the different ecophysiological groups in Iran (Akbarpour et al., 2021)
and Argentina (Gonzalez et al., 2009). Kim et al., (1994)
reported that the degree of pungency is positively correlated with alliin content.
Detection of phytochemicals revealed that only flavonoids and phenols are present in all the garlic varieties studied (Table 5).
Table 5: Qualitative phytochemical analysis of eight garlic accessions.
Similarly, Arify et al., (2018)
confirmed the presence of phenols and flavonoids and the absence of tannins in garlic accessions from India. Strati et al., (2018)
species, especially garlic and leek, to be generally rich in phenols and flavonoids. Phenols are considered responsible for the pungency of garlic, while flavonoids influence the stability of Allium
spp. when cooked and stored (Lanzotti, 2006)
Molecular analysis-SSR markers
Three primers were able to amplify five DNA fragments, three monomorphic and the other polymorphic. ASA-08 primer generated only one monomorphic band at 250 bp while ASA-10 produced two at 250 and 150 bp. On the other hand, two polymorphic bands were detected at 250 and 225 bp in the ASA-24 primer amplification profile (Fig 3).
Fig 3: Banding patterns of garlic varieties, including other Allium spp. accessions using SSR markers.
This runs contrary to the results obtained by Kumar et al., (2018)
where ASA-24 primer failed to amplify any DNA fragment and Anwar et al., (2020)
where ASA-10 primer was found to be highly polymorphic. Furthermore, it is only in Batanes White that ASA-24 primer was not able to generate any DNA fragment at all amplicon sizes while MMSU Gem is the only accession that has one polymorphic band amplified by the same primer. Thus, only one primer, ASA-24, can be used to discriminate Batanes White and MMSU-Gem among the NSIC-registered varieties and landraces of garlic in the Philippines and could be used to delineate the registered varieties.