Roll 20 Needle Blight: A Fungal Pathogen Threatening Pine Seedlings

Mycosphaerella gibsonii, commonly known as roll 20 needle blight, is a fungal pathogen that affects pine seedlings, causing significant damage to the trees and hindering their growth. This disease is a major obstacle to the production of high-quality pine seedlings, which are essential for reforestation and sustainable forestry practices.

The fungus produces spermatia on conidiogenous cells lining the inner wall of locules, which are hyaline, rod-shaped, and measure 2-3 x 1 micrometers. The spermagonia form in discrete, unilocular stromata or as locules in upper parts of large stromata. Ascospores are hyaline, one-septate, ellipsoidal to cuneate, measuring (7.5-) 8.5-11 (-12.5) x 2-3 micrometers.

Asci are bitunicate, clavate to cylindrical, with a thickened, bluntly rounded apex and obliquely biseriate eight spores. Conidia are pale yellowish-olivaceous, long-obclavate, straight or slightly curved, with three to seven septa and measuring 20-68 x 2.5-4.5 micrometers.

The fungus can be cultured on potato carrot agar (PCA) at 25°C or on V8 juice plus pine needle decoction agar in natural light at the same temperature. Higher night temperatures cause abnormal conidial formation, while gibsonii can also be grown on PCA-UV at 25°C.

Gibsonii is listed as an A1 quarantine pest in the EPPO region and is considered of quarantine significance in South America. The disease is spread through natural dispersal by wind and water, but international movement of infected nursery stock is a major contributor to its spread.

Prevention is key in controlling the spread of roll 20 needle blight. Phytosanitary control measures such as avoiding the planting of infected plants, removal and destruction of all infected pines in nurseries, and cleaning between annual production cycles can help reduce the spread of the pathogen.

The disease eventually causes needle necrosis and needle cast, leading to defoliation, stunted growth, and host plant death. Lesions appear on needles, initially affecting lower needles before spreading to the upper crown. Roll 20 needle blight is a significant threat to pine seedling production, and prompt action is necessary to prevent its spread and mitigate its impact.

In summary, roll 20 needle blight is a fungal pathogen that affects pine seedlings, causing significant damage to the trees and hindering their growth. Prevention is key in controlling the spread of the disease, and phytosanitary control measures can help reduce its impact. Early detection and prompt action are necessary to prevent the spread of roll 20 needle blight and ensure the production of high-quality pine seedlings.