Heat Stress and Broccoli Appearance of the head is a key quality indicator in broccoli. While excessive heat is not a common problem on the Canadian prairies, growers should nonetheless be aware of the potential impact of heat stress on their broccoli crops. Sensitivity to heat stress has a strong genetic component. Farnham and Bjorkman (2011) have recently shown that many of the most widely grown cultivars of broccoli (cv. Marathon, Greenbelt, Arcadia and Patron) were all more susceptible to heat stress than new lines bred specifically for enhanced heat tolerance. Under extremely hot conditions (avg. high > 30C, avg. low> 20C) these cultivars failed to form a marketable main head and instead produced a mass of lateral branches. Under less extreme conditions head quality was compromised by heat stress – the heads became flattened, with a pale color and uneven bead size.
Source: Farnham and Bjorkman (2011). HortScience 46: 858-863.