It may be over 30 years since the courgette variety Ambassador first came onto the market but it continues to be the mainstay for the industry - and it is the standard against which varieties in the first National Institute of Agricultural Botany (NIAB) courgette trial for several years are being compared.
But the 18 other green varieties, plus one yellow and one round-fruited variety in the trial at NIAB's headquarters outside Cambridge - by no means the complete range that is available - show what newer breeding can offer in terms of fruit quality, plant habit and disease tolerance.
Where virus infection is an issue for some growers - quickly spread by aphids or by cutting, rather than twisting, fruit at harvest - newer varieties with virus tolerance may be worth investing in, says Clause UK development and product marketing manager John Ward.
But he points out that in comparison to, for example, Ambassador, there will be a trade-off with yield. "In a strong virus environment you need the newer varieties with the complete disease-resistance package," he says. "You tend to lose yield but it protects you against the bad years."
Sown on 21 May and planted on 9 June, the first harvest was 10 July for most varieties. Mikonos and Syros were both a couple of days later into pick. Fruit was harvested three days a week and, for the purposes of the demonstration, in two sizes of 10-14cm and 14-22cm. With yields equivalent to 8.8 tonnes/ha in the first two weeks of picking and 15.1 tonnes/ha in the second two-week period, Ambassador showed why it is still such a growers' favourite.
In this trial Mikonos, Naxos, Quine, and Precioza had lower yields in both periods. Syros, Cora, Tosca, and SQ-H2 had a higher earlier yield while Dunja, XSD 2846, TZ9155 (marketed as Midnight) and TZ9123 had similar early yields, but none could quite match Ambassador at four weeks.
The trial did demonstrate, however, that the commercial standard can be trumped on yield, at least on NIAB's medium silt, with Firenze coming in at 11.3 tonnes/ha at two weeks and 17.2 tonnes/ha at four weeks, and Enza's coded variety E82.205 at 10.8 tonnes/ha and over 20 tonnes/ha.
Of these two high yielders, E82.205 was more closed in habit. Its fruit are darker, slightly ridged and difficult to cut, and they had a larger blossom scar. Firenze, from Tozer Seeds, has an open plant habit, which helps picking, but had started to trail by the time of the demonstration's open day on 25 August.
TZ9123, also from Tozer, had a similarly open habit but was beginning to trail a little and its fruit were noticeably short-stemmed. Fruit from TZ9155 were darker and more difficult to cut.
"The flowers liked to hold on quite tightly and there was a bit of snapping of the tips of the baby fruit," says NIAB vegetable specialist Bruce Napier.
TZ9155 was the most compact of all the varieties in the trial. In other trials conducted for Tozer, this variety has beaten Ambassador on yield by 15 tonnes/ha by mid-June from a mid-May planting and was judged to have more elongated fruit, which would suit processing.
The four green-fruited varieties submitted by Syngenta have resistance both to cucumber mosaic virus and zucchini yellow mosaic virus, the two main virus problems in the UK.
The fruit of Mikonos are slightly curved. Quine fruit were nicely shaped, with the flower coming off easily to leave a small scar. Syros has a darker fruit than some other varieties, was easy to cut and the plant had an open habit although leaves were spiny. Naxos has slightly ridged fruit with a large flower scar but was easy to cut.
"Comments from my European colleagues suggest Naxos likes a bit of heat and performs better as a second crop," says Syngenta vegetable sales specialist Chris Lee. He says Syngenta has a wide range of varieties from Europe to test for UK conditions and is looking out for those particularly suited to baby fruit production.
Clause's trio of Cora, Tosca and Precioza all had little blossom scarring. Napier describes Cora as one of the spinier varieties, with slight ridging that was more obvious on the baby fruit. Tosca was the easiest to cut out of the pair. "Precioza had slightly more curved fruit but not to the extent of being rejected," says Napier. "It also didn't hold onto its flower."
Tosca and Cora, which is normally used for early production because it is a little faster, are widely grown in western Europe in those regions where virus pressure is lower, says Ward. "Precioza has a full resistance package but you get a knock on the yield," he adds.
Sakata's variety SQ-H2 showed some slight curving on the baby fruit. XSD 2846 from the same breeder produced paler fruit than some varieties with slight ridging. Flower retention was weak and the blossom scar small.
Two Seminis varieties were planted 14 days later than the main trial, on 23 June from a 12 June sowing, but had come into pick by 20 July. Compared with Ambassador planted at the same time - which yielded the equivalent of five tonnes/ha at two weeks and 9.3 tonnes/ha at four weeks - Quirinal, which has zucchini yellow mosaic virus resistance, had a higher early yield and a similar later yield. Its fruit are held upright and so are easy to cut.
Valiant, which has been re-named Acceste, yielded better all-round with almost 20 tonnes/ha at four weeks. "Acceste has quite a long stem, which helps with cutting," says Napier.
Powdery mildew began to make an appearance in the plots in mid-August. Most varieties look susceptible based on NIAB's observations but Naxos, Tosca, Dunja and TZ9123 had less mildew than average.
One paler variety - which was submitted by Elsoms and known only as "courgette 2" - yielded more heavily than Ambassador. But it was also noticeably freer of mildew, which is why the company is targeting this variety for organic production.
YELLOW AND ROUND
The sole yellow-fruited variety in the trial, Golden Delight from Syngenta, was comparatively low yielding. "Fruit were slower to fill," says Napier. "They were slightly curved and brittle."
The round fruit of Brice, also from Syngenta, were hard to approach when the plants were young, with fruit sometimes shearing off. Napier says fruit were difficult to cut but became easier to twist off. The variety also tends to hold onto the flower, which can rot on the fruit.
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