Tolypothrix tenuis

Tolypothrix tenuis is a filamentous cyanobacterium that, while beneficial for soil nitrogen fixation, can act as a problematic organism in paddy rice cultivation. Under certain environmental conditions, its overgrowth creates significant physiological stress for rice plants, classifying it as a factor contributing to yield loss in aquatic agricultural systems.

The core of the problem lies in the formation of dense, floating algal mats on the water surface. These mats physically obstruct sunlight from reaching the submerged parts of the rice plant and effectively compete for dissolved nutrients. Furthermore, the decay of excess algae can lead to oxygen depletion in the rhizosphere, hindering root respiration.

Visible signs of infestation include the appearance of green or bluish-green scum on the water surface. Affected rice plants exhibit stunted growth, chlorosis, and delayed tillering. Because the algae block gas exchange, the roots often turn dark and fragile, which severely impairs the plant's ability to absorb essential micronutrients from the soil.

The development and proliferation of Tolypothrix tenuis are favored by high light intensity, shallow stagnant water, and elevated water temperatures (typically between 25°C and 32°C). High phosphorus content in the irrigation water, often resulting from agricultural runoff or fertilizer application, acts as a primary catalyst for rapid blooms.

Recommended strategies to mitigate the impact include:

• Adjusting fertilization schedules to prevent phosphorus accumulation in surface water.
• Implementing water management practices, such as periodic drainage, to disrupt the algal growth cycle.
• Utilizing selective, rice-safe algicides to control severe blooms during the early vegetative stages.
• Encouraging rapid crop canopy closure to reduce light penetration to the water surface, thereby naturally suppressing algal photosynthesis.