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INTRODUCTION

Tuberose (Polianthes tuberosa Linn.) is an important tropical bulbous ornamental plant belonging to the family ‘Asparagaceae’ and is native to Mexico (Bailey, 1919). There are two types of tuberose namely, Single and Double which are commercially cultivated across the globe for their exquisite flowers. Single types are used as loose flowers for garland purpose and perfumery industry whereas double varieties are highly preferred for cut flower and bouquets because of the longer keeping quality of the flower spikes. Double tuberose flowers have high demand in both local and international markets and are being exported to gulf countries. The increasing demand for superior and novel double type tuberose necessitates the development of varieties of this category. Tuberose is commercially cultivated in India in an area of about 16,190 ha, with a loose flower production of 1, 07, 910 metric tonnes and cut flower production of 89.29 lakh numbers of cut stems (Anon, 2016). Root knot nematode infects tuberose and leads to 10-14% of crop loss (Khan and Reddy, 1992). Leaf blight disease caused by Alternaria polianthi is extensive in tuberose growing regions of the country. Development of tolerant and resistant varieties to these biotic stresses is the need of the hour to help the tuberose growers. Keeping these objectives in view, an advance breeding line of double type tuberose (IIHR-4) developed by ICAR-IIHR was evaluated for flowering, yield, quality and reaction to root knot nematode and A.polianthi leaf blight disease.

MATERIALS AND METHODS

The investigation was carried out at the Division of Flower and Medicinal Crops, ICAR-Indian Institute of Horticultural Research, Bengaluru during 2015 - 2018. The advance breeding line of tuberose IIHR-4 with double flowers was evaluated along with the commercial check varieties Arka Vaibhav, Arka Suvasini, local checks Hyderabad Double and Pearl Double. Randomized block design was followed for the experiment with three replications. Uniform size of bulbs (2.5 cm diameter) were planted on raised bed with the spacing of 30 x 30 cm. Standard cultural practices were followed throughout the experimental period. The growth, yield and quality parameters viz., days to spike emergence, days to opening of first floret, spike length, rachis length, number of florets per spike, length of floret, diameter of floret, bud length, matured bud weight, single flower weight, number of spikes per clump, vase life, number of bulbs per clump, number of bulblets per clump, internodal length between the florets and number of florets open at a time on the rachis were observed. The tuberose lines/cultivars were screened for the tolerance/ resistance against root knot nematode Meloidogyne incognita for three consecutive years. Gall Index (GI) was recorded in the roots in a 0-5 scale as per Taylor and Sasser (1978) at the time of bulb harvest. Per cent disease index and host reaction of tuberose genotypes against leaf blight disease caused by A. polianthi under field condition was recorded thrice at15 day interval using 0-5 scale (Narayanappa and Chandra, 1984). The pooled data of three years were statistically analyzed as per Gomez and Gomez (1984).

RESULTS AND DISCUSSION

The results of the study revealed significant differences among the tuberose lines for flowering and yield parameters (Tables 1 and 2). Days to spike emergence ranged from 133.73 (Arka Suvasini) to 198.00 (Pearl Double) with the general mean of 161.53 days. The advanced breeding line IIHR-4 recorded 154.15 days to spike emergence. Early spike appearance in tuberose cultivar Arka Suvasini was reported by Safeena et al. (2019) who noticed wide range of variation in days taken to flowering due to variation in genetic makeup and prevailing environmental conditions. Spike length ranged from 62.00 cm (IIHR-4) to 86.36 cm (Pearl Double) with the mean of 78.64 cm. The advanced breeding line IIHR-4 recorded spike length of 62.00 cm with upright stalk categorized into short spike group suitable for cut flower. Varietal differences for spike length was earlier reported by Madhumati et al. (2018), Prashanta et al. (2016), Safeena et al. (2019) and Dogra et al. (2020) in tuberose. Rachis length varied from 25.59cm (IIHR-4) to 33.71cm (Arka Vaibhav) with the general mean of 29.06 cm. The number of florets per spike was recorded the maximum in Arka Suvasini (55.33) and minimum in Pearl Double (48.78) with the mean of 50.91. The results are in line with findings of Ranchana et al. (2013), Rao and Sushma (2015), Bharathi et al. (2018) in tuberose and Rani and Singh (2005) in gladiolus. The variation observed in spike length and rachis length might be attributed to the inherent genetic characters of the individual cultivars and environmental factors.

The line IIHR-4 recorded least floret length of 5.22 cm and Arka Suvasini recorded the highest floret length of 6.22 cm with the general mean of 5.69 cm. Similar results on highest floret length of tuberose cultivar Arka Suvasini was stated by Ranchana et al. (2013). The florets of IIHR-4 are short and arranged closely without any gap between the internodes, making the spike very attractive and rendering the line highly suitable as cut flower. Such variation might be due to the varietal characters and similar observations were made by Bharathi and Umamaheswari (2018).

Diameter of floret varied from 4.44 cm (Pearl Double) to 4.77 cm (Arka Suvasini) with the general mean of 4.56cm. This may be due to varied growth rates and genetic make-up. The results are in line with the findings of Rao and Sushma (2015) and Gandhi et al. (2017) and Safeena et al. (2019) in tuberose. Bud length ranged from 4.86 cm (Hyderabad Double) to 5.68 cm (Arka Suvasini) with the mean of 5.40 cm. Single flower weight was varied from 2.29g (Arka Vaibhav) to 3.57g (Arka Suvasini) with the mean of 2.73g. The variation in floral parameters might be primarily governed by the genetic makeup of the varieties and these results were also experimentally supported by the findings of Andrew et al. (2017).

Number of florets open at a time on the spike is an important trait for cut flower spike since it depicts the exquisiteness of the cut flower. The line IIHR-4 recorded the highest number of florets (7.10) open at a time on the spike. The lowest was observed in Arka Vaibhav (2.40) with the general mean of 4.50. The advanced breeding line IIHR-4 was very appealing with highest number of florets open at a time on the spike and this character makes the line IIHR-4 highly suitable as cut flower, especially for flower arrangement and bouquet (Fig.1). The line IIHR-4 was found to be superior over the commercial check for the above character. The variations in number of florets open at a time on the spike might be due to different genetic make-up of the different cultivars and prevailing environment conditions of the experimental area. The results are in conformity with the findings of Kusum (2010) in tuberose who also reported the variation among the tuberose cultivars for the maximum open florets per spike.

According to Bharathi and Umamaheswari (2018), the trait internodal length indicates compactness of the florets arranged on rachis, which is the ideal character for the selection of suitable cut flower. In the present investigation, internodal length between florets ranged from 3.45 (IIHR-4) to 5.79 cm in Arka Vaibhav with the general mean of 4.54 cm. Among the double types evaluated, the line IIHR-4 recorded the shortest internodal length and the florets are arranged very densely on the spike. In agreement with findings of the present study, the highest internodal length in Arka Suvasini was reported by Singh and Singh (2013) in tuberose under Delhi condition. Variation in the internodal length might be due to the genetic makeup of the cultivars under study and similar observations were reported by Bharathi and Umamaheswari (2018) in single type tuberose.

Number of spikes per clump ranged from 2.14 (Hyderabad Double) to 4.43 (IIHR-4) with the mean of 3.23. Number of spikes per m2 varied from 19.24 (Hyderabad Double) to 33.94 (IIHR-4) with the mean of 26.52. This variation in spikes per clump is in line with the findings of Rao and Sushma (2015), Ranchana et al. (2013), Gandhi (2017) and Safeena et al. (2019) in tuberose. Number of spikes per hectare ranged from 1,92,750.00 (Hyderabad Double) to 3,98,781.25(IIHR-4) with the mean of 2,90,481.25.

The advanced breeding line IIHR-4 was found to be superior in flower yield than the commercial check Arka Vaibhav. This variation in the production of spikes/plant and spikes per plot might be due to the genetically controlled factor and also due to the hereditary traits of different cultivars under prevailing environment.

The vase life ranged between 6.50 and 7.25 days for the genotypes evaluated. Significant differences were not noticed among the double genotypes for vase life indicating that the advanced breeding line IIHR-4 has good vase life and it is on par with commercial cultivars interms of vase life.

Arka Suvasini recorded minimum number of bulbs per clump (2.69) and maximum number of bulbs per clump was recorded in Arka Vaibhav (8.19) with the mean of 5.14. Number of bulblets per clump ranged from 32.81 (Arka Suvasini) to 71.00 (Pearl Double) with the mean of 53.28. The variations in bulb parameters might be due to the presence of genetic variability of the cultivar and the results are in line with the findings of Madhumathi et. al. (2018) in tuberose. With respect to straightness of spike, the line IIHR-4, Arka Vaibhav and Hyderabad Double were found to bear straight spikes, while the cultivars Arka Suvasini and Pearl Double produced slightly bent spikes. The tinge on flower bud was recorded to be green in the line IIHR-4 and Arka Vaibhav and all the other cultivars recorded pink tinge on flower bud. The type of flower opening was found to be shy in Pearl Double while all the other cultivars recorded wide flower opening. Differences in nature of spike, flower opening and tinge on flower bud was earlier reported by Bharathi and Umamaheswari (2018) in tuberose and these are due to the distinguished generic make up of the genotypes.

The advanced breeding line IIHR-4 was screened for the tolerance/ resistance against root knot nematode M. incognita for three consecutive years and the pooled analysis revealed that it was highly resistant under field conditions with least gall index of 1.24 (Fig. 1). Variations of tuberose genotypes for root knot nematode tolerance and resistance were reported earlier by Gandhi et al. (2018) who stated that this might be due to the inherent genetic character. Per cent disease index and host reaction of tuberose genotypes against leaf blight disease caused by Alternaria under field conditions were recorded and the results indicated that the breeding line IIHR-4 has better field tolerance to Alternarialeaf blight as compared to the other tuberose genotypes evaluated (Fig. 3).

CONCLUSION

It is concluded from the above study for three consecutive years that among the cultivars evaluated for flowering, yield, quality and biotic stresses, the advanced breeding line IIHR-4 with superior flowering and quality parameters namely the double type florets on shorter spike and rachis, more number of florets open at a time on the spike, shorter intermodal length between the florets with compact floret arrangement, straight spikes with wide open florets and green tinge on flower buds makes the IIHR-4 as most ideal cut flower cultivar. It was also found to be highly resistant to root knot nematode M. incognita under field conditions with better field tolerance to Alternaria leaf blight disease.

REFERENCES

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