new hybrid

Ever since the discovery of Lathyrus belinensis in 1987, breeders have been trying Developing to create a yellow-flowered a yellow sweet pea. sweet pea

Dawn Edwards discusses The first offspring, OB1 (centre), the latest developments and provides resulting from the cross between L. odoratus ‘Mrs Collier’ (left) a name for the first hybrid and L. belinensis (right)

ince its introduction into Promising new species have a red pigment spot at their base cultivation in the 17th century However, the discovery in 1987 of which is not present in L. odoratus, S from Sicily, intraspecific a new annual species, L. belinensis, in and that L. belinensis has membran­ breeding of Lathyrus odoratus (sweet Antalya, Turkey (Maxted & Goyder ous, indehiscent fruit, whereas in pea) has yielded a vast number of 1988) has given new hope to breeders. L. odoratus the fruit is dehiscent. cultivars. These range in flower This species has yellow pigment in colour from white through shades its flowers, with red-veined, orange- of cream, pink, orange, red, blue yellow standards and yellow wing and mauve, to dark purple. Conspic­ and keel petals. Also, morphologic­ uously missing from this palette, and ally it is the closest relative of much desired by gardeners, is yellow. L. odoratus, with few vegetative This is not for a lack of trying by characters separating the two species. breeders, but traditional breeding Most noticeably, L. odoratus has an methods are unlikely to lead to a indumentum of prominently tuberc­ yellow-flowered sweet pea. Attempts ulate hairs, whereas L. belinensis is All photographs by Keith Hammett have been made to cross L. odoratus glabrous or glabrescent on the stem with other species of Lathyrus that with inconspicuously tuberculate OB1, the first hybrid between have yellow flowers, but hybrid­ hairs on its side shoots and fruit. L. belinensis and L. odoratus, ization mostly failed or did not result Hammett et al. (1994) also found being grown on in culture after embryo rescue in yellow-flowered progeny. that seedling leaflets of L. belinensis

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First crosses description initially limited because backcrosses

In anticipation that the close using the F1 plants could only be relationship between these two Lathyrus x hammettii achieved with wild L. odoratus. species might enable successful D. Edw., hybr. nov. However, backcrosses with hybridization and lead to a yellow- Garden hybrid between L. odoratus cultivars have now been flowered sweet pea, Dr Keith L. belinensis Maxted & Goyder successful, resulting in robust, fertile Hammett, a leading sweet pea and L. odoratus L. A small, seedlings with previously unseen breeder, and co-workers undertook pubescent, annual plant to 50cm colours, but no yellow yet. Work a breeding programme. Breeding tall, with leaves comprising 1 pair is ongoing with the L. belinensis barriers were encountered and a of green leaflets to c.2.5cm long, breeding line in the hope that a number of attempted crosses failed, ending in green, 3-branched yellow sweet pea can be raised. or produced plants that failed to tendrils. Standard petal pink reach maturity. (186B/55B) fading to cream (1D) A new hybrid A successful cross was eventually at the base, c.2.5cm long, I therefore propose a hybrid epithet made using L. belinensis as the reflexed, emarginate; wing petals for the cross between L. belinensis and pollen parent and cream-flowered violet (94B/87A) over cream L. odoratus. At the suggestion of L. odoratus ‘Mrs Collier’ as the seed (1D), becoming yellowish green garden writer Graham Rice I am parent. This was achieved using (145C) at the upper edge, c.2cm naming it Lathyrus x hammettii in embryo rescue technology, a long; keel petals cream (4D). honour of its creator, Dr Keith laboratory technique that aids the Scent strong, but neither as sweet Hammett, and his contribution development of embryos that might as L. odoratus nor as sharp as to Lathyrus breeding. otherwise have aborted. The embryo L. belinensis. Self-sterile, partly Hammett, based in New Zealand, is dissected out of the seed before male-fertile. Further variation works on a number of plants, maturity and grown on in a resulting from backcrossing is particularly dahlias and sweet peas. culture medium. described under each cultivar The revival of interest in bicoloured The resultant hybrid, referred raised to date (pp253–254). sweet peas resulted from his intro­ to as OB1 by the breeders, lacked Type: cultivated plant raised by duction of these colours into modern hybrid vigour and was a weak plant, K Hammett, Massey, Auckland, cultivars in the second half of the shorter than both parents and with New Zealand, from rescued 20th century. He then took this smaller leaves. Intermediacy embryo excised on 28 Dec 1991 further with the creation of reverse between the parents was evident in (holotype: AK, specimen no. bicoloured flowers. In contrast to both flower size and scent, with the AK212042, 19 Jan 1993). bicolours these have wing petals that latter intermediate between the Colour references are taken are darker than the standards. The sweet scent of L. odoratus ‘Mrs from Hammett et al. (1994) who cultivar ‘Erewhon’, which belongs Collier’ and the sharp scent of used the RHS Colour Chart (1966). to this hybrid, is perhaps the most L. belinensis. In the parents and striking example to date. the offspring the scent was strong. but again produced pink and violet The formal description of the Curiously, however, considering flowers (K Hammett, pers. comm.). hybrid is based on the type specimen. the flower colour of the parents, Both of the initial F1 hybrids were However, intense backcrossing in the hybrid had a pink standard and self-sterile and the plants lasted 19 the quest for yellow-flowered and violet wing petals. It resembled a and 18 months respectively. This is other gardenworthy cultivars has paler version of wild L. odoratus, in contrast to the fertile, annual already led to considerable variation which has maroon standard and parent species which normally have a from this description, and is likely purple wing petals. 9-month lifespan. The initial F1 to continue to do so. Subsequently, the cross was hybrids were partly male-fertile, achieved without embryo rescue which enabled backcrossing with Lathyrus x hammettii cultivars using L. belinensis as the seed parent both L. odoratus and L. belinensis. Six cultivars already released into and orange-flowered L. odoratus Cultivars resulting from cultivation are described here. ‘Orange Dragon’ as the pollen backcrossing with L. odoratus are ‘Blue Shift’ – flowers open mauve, parent. Known as A18, this second now commercially available. developing to an intense blue. hybrid was more robust than OB1, Variation in the breeding line was ‘Blue Vein’ – flowers open ➤

December 2014 253 new hybrid

Cultivars of Lathyrus x hammettii have vivid colours, but no yellow yet; ‘Blue Vein’ (left), reverse bicolour ‘Erewhon’ (right) and ‘Porlock’ (below) apricot, turning a paler orange, with Dancer’) – cream petals edged with a strong marbling of dark blue veins. rosy pink. This cultivar was derived from ‘Porlock’ – crimson standard and backcrossing of A18. dark mauve wings with marbling ‘Erewhon’ – the most strongly caused by prominent dark maroon contrasting reverse bicolour to date, veins. This cultivar was derived from with pinkish lavender standards set backcrossing of A18. against darker, mauve wings. It was ‘Turquoise Lagoon’ – flowers open named after Erewhon, a novel by pale pink, maturing to a vibrant Samuel Butler describing a fictitious turquoise. land where features of life are in reverse. Conclusion ‘Painted Porcelain’ (syn. ‘Spanish Hammett’s breeding programme has already given rise to a number of references cultivars with previously unseen Hammett, KRW, Murray, BG, colours and colour combinations, Markham, Kenneth R & Hallett, IC (1994) Interspecific hybridization and more are in the pipeline. between Lathyrus odoratus and Furthermore, the exciting possibility L. belinensis. Int. J. Plant Sci. 155(6): remains that continued backcrossing 763–771 involving L. belinensis will eventually acknowledgements Maxted, N & Goyder, DJ (1988) lead to the coveted yellow-flowered I would like to thank Keith A new species of Lathyrus sect. sweet pea. Hammett for information on his Lathyrus (Leguminosae — Papilio­ breeding programme and Graham noideae) from Turkey. Kew Bull. Dawn Edwards is a botanist at Rice for alerting me to the need for 43(4): 711–714 RHS Garden Wisley a name for this hybrid.

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