Effects of smoke, red light, potassium nitrate and alternate temperature on seed germination of Laggera alata and Laggera crispata forms

Species within the genus Laggera Sch. Bip. Ex. Benth. & Hook hold significant potential in the food, cosmetic, and pharmaceutical industries. However, their cultivation is limited by reliance on wild collection and poorly understood germination requirements. This study examined the germination responses of Laggera alata with small capitulum (LA-SC), Laggera alata with big capitulum (LA-BC), Laggera crispata from South Africa (LC-SA), and Laggera crispata from Zimbabwe (LC-ZIM) to smoke and potassium nitrate (KNO₃), smoke and red light, and alternating temperatures. Treatments were applied to 25 seeds per Laggera form, sown in Petri dishes with four replications per treatment, and analyzed using Analysis of Variance. Results showed that smoke treatment significantly enhanced germination percentage across most Laggera forms, particularly LA-BC. The combination of smoke and KNO₃ synergistically improved germination in LA-BC and LC-SA but had a negative effect on LC-ZIM. Red light exposure increased germination percentage from 10 to 69% in LA-SC and accelerated germination in LC-SA, which otherwise failed to germinate in darkness. Additionally, red light shortened germination time in LC-ZIM and LA-SC from 11 days to 6 and 5 days, respectively. Temperature played a crucial role, with a constant 30 °C promoting the highest germination percentages, while 10 °C completely inhibited germination. This research offers important insights to guide the propagation of the Laggera species from seeds for agricultural production.