Aggregatum group includes shallots and potato onions and are referred to as multiplier onions. The bulbs are smaller than those of common onions, and a single plant forms an aggregate cluster of several bulbs from a central bulb. They are propagated commercially from daughter bulbs, and varieties which set seeds under TamilNadu conditions are propagated through seeds. Shallots are the most important subgroup within this group and comprise the only cultivars cultivated commercially. They form aggregate clusters of small, narrowly ovoid to pear-shaped bulbs. Potato onions differ from shallots in forming larger bulbs with fewer bulbs per cluster, and having a flattened (onion-like) shape. Intermediate forms exist [5].

Diversity in plant genetic resources offers plant breeders the opportunity to develop novel and better cultivars with desirable characteristics, which include both farmer-preferred traits like yield potential and larger bulbs and breeder-preferred traits which include pest and disease resistance and photosensitivity [6]. The conservation of germplasm is necessary for maintaining genetic diversity, studying local genetic material and under-utilized species, and to choose species suitable for developing newer varieties [3]. No country in the world is self-sufficient in germplasm to fulfill its food requirements. Many countries predominantly depend on nonindigenous crops and imported germplasm for food and agricultural development [4].

Aggregatum onion (Allium cepa var. aggregatum) is mainly grown in Tamil Nadu, Andhra Pradesh and Karnataka. In TamilNadu it is cultivated in an area of 30,000 ha. It is well known for its use in sambar preparation, an important South Indian dish. It has demand in the international market due to its unique taste and flavor. Inorder to identify genotypes which perform better in terms of quality and yield, this study has been undertaken to evaluate the performance of genotypes available.

2.Materials and methods

The present study was conducted at the College Orchard of the Department of Vegetable Science, Horticultural College and Research Institute, Tamil Nadu Agricultural University, Coimbatore during 2021-2022. A total of 65 genotypes maintained at the Department of Vegetable Science were evaluated for yield, quality parameters, and disease index. (Table.1) The experiment was laid in randomized block design with two replications. The package of practices as recommemded by the crop production guide of TamilNadu was followed. Observations were recorded on Average bulb weight (g), Total Soluble Solids (%), Total Yield (t/ha),thrips damage(%), leaf spot (PDI) and Stemphyllium blight (PDI). Ten plants were randomly selected from each plot for recording data and the average was calculated. After curing, the total bulb fresh weight was measured for each plot. The total soluble solids (TSS) content of bulbs were recorded by hand refractometer. The disease (leaf spot and Stemphyllium blight) severity of onion was scored by following 0-5 scale, as described by [8]. The details of scales are as follows: 0-no disease symptoms, 1- a few spots towards tip covering 10% leaf area, 2- several dark purplish brown patch covering up to 20% leaf area, 3- several patches with paler outer zone covering up to 40% leaf area, 4- leaf streaks covering up to 75% leaf area or breaking of the leaves from center and 5- complete drying of the leaves or breaking of the leaves from the centre. Likewise, thrips infestation was also rated by following 0-5 scale. Observations were made at the first appearance of disease symptoms/thrips on plants, till the harvest at weekly intervals. Color of bulbs were identified by visual assessment method.

3.Results and Discussion

The genotypes used in the study exhibited a wide range of differences in the parameters measured. The observations recorded are given in Table 2.

3.1. Bulb weight

There were significant differences in bulb weight among the different genotypes (Table 2). The heaviest bulb weight (66.2g) was observed in the genotype Agg-Sel-1 followed by followed by Agg-Sel-3 with 64.4g. The lightest individual bulb (33.2 g) was observed in Agg-1519. The difference in bulb weight could be attributed to the genetic potential of the different genotypes. The results of the present study confirms with the findings of [9].

3.2.Total soluble solid content

The total soluble solids (TSS) content differed significantly among. The highest percent of Total Soluble Solids (15.3) was recorded in Agg1552 followed by Agg 1535 with 15.2% and Agg-Sel-4 with 15.0%. The lowest TSS content (7.0%) was observed in 1548-Agg.The variation in TSS content among the genotypes might be attributed to differences in the genetic potential of the genotypes used in the study. This is following the results of [1].

3.3.Yield

The genotypes expressed significant variation in yield per hectare. The genotypes, Agg 1522 and Agg 1692 recorded a total yield of 17.4t/ha which was higher than all other genotypes. The lowest yield per hectare (6.80t/ha) was observed in Agg-Sel-43 followed by Agg 1523 with 10.5t/ha. The superior performance of the genotypes could be due to their higher individual bulb weight. Similar results have been obtained by [2,7,10].

3.4.Skin and flesh colour of the bulb

 The result of color measurement revealed that there was not much variation in the skin colour of the bulbs among the different genotypes evaluated.

3.5.Disease incidence and thrips infestation

The genotypes evaluated also showed significant differences for disease scoring. The lowest percent of thrips (12.5) was observed in Agg 1528, the lowest leaf spot incidence was observed in Agg1532 with 11.5 and the lowest incidence of Stemphyllium blight was recorded in Agg-Sel-2 with 3.7.The apparent cause of the variation in disease severity and pest infestation expressed by the different genotypes might have been due to their genetic potential.

4.Conclusion

Based on the present study it can be concluded that the genotypes, Agg-Sel-1, Agg-Sel-3 Agg 1522, and Agg 1692 recorded higher yield compared to other genotypes and the genotypes, Agg 1528, Agg1532 and Agg-Sel-2 showed lesser disease incidence and pest infestation. Hence these genotypes showing better performance can be utilized for further breeding programmes.

Declaration of competing interest

The authors declare that they have no conflict of interest.

Declaration of generative AI and AI-assisted technologies in the writing process.

The authors declare that they have not used AI tools in the writing process.

Author contribution

Usha Nandhini Devi Harinarayanan – performed the experiment, interpretation of results, manuscript preparation

Pugalendhi Lakshmanan – conception, supervision, Project administration, and Fund acquisition

Acknowledgement

The authors greatly acknowledge the Directorate of Onion and Garlic, Rajagurunagar, Pune, Maharashtra for providing funds to undertake this study.

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