Hoja Blanca, meaning “white leaf” in Spanish, is a plant disease that affects rice crops. It is caused by the rice hoja blanca virus (RHBV), a plant virus from the Phenuiviridae family. The virus can stunt rice plant growth or, in severe cases, lead to death, threatening agricultural yields.
Recognizing the Disease
Symptoms of Hoja Blanca Virus (HBV) on rice plants follow a distinct pattern. Early signs appear as cream-colored, elongated spots on immature leaves within four days of infection. These spots expand, forming yellow or pale green mottling that eventually turns white.
Discoloration progresses into chlorotic stripes, and later leaves may become entirely white. Infected plants exhibit stunted growth and reduced tillering, meaning fewer side shoots develop. Panicles (flower clusters) may be sterile or malformed, showing discoloration and a “parrot beak” deformation of florets. Grains may also be incompletely filled, reducing yields. Roots of diseased plants are reduced in size and number, turn brown, and die.
How the Disease Spreads
Hoja Blanca spreads through an insect vector, the rice delphacid, Tagosodes orizicolus. This planthopper acquires the virus when it feeds on an infected rice plant. The virus multiplies within the insect, making it infectious for life.
This is a persistent propagative transmission, meaning the virus replicates inside the vector. After acquiring the virus, there is an incubation period ranging from 4 to 31 days before it can transmit the virus to healthy plants. The rice delphacid can also transmit the virus to its offspring through transovarial transmission, meaning infected females pass the virus to their offspring through eggs.
Impact on Agriculture
Hoja Blanca outbreaks have historically led to agricultural losses in tropical and subtropical American rice-producing regions. The disease can cause yield reductions ranging from 25% to 75% in susceptible varieties. In severe epidemics, losses can reach 100%.
These losses have economic repercussions for farmers and affected countries. For instance, in 1956, Cuba and Venezuela saw yield losses of 25% and 50%, respectively. The disease’s widespread crop damage impacts local and national food supplies, threatening food security.
Control and Prevention Strategies
Managing Hoja Blanca involves strategies to reduce the virus and its insect vector. A primary approach is developing and using rice varieties resistant to the virus or the rice delphacid. Breeding programs have transferred resistance genes from japonica rice into indica varieties suitable for Latin American cultivation.
Controlling the rice delphacid population is also important. While insecticides are used, their effectiveness against the virus can be limited, as even low numbers of infected insects can trigger an epidemic. Cultural practices, such as synchronized planting, disrupt the vector’s life cycle by creating periods without susceptible host plants. Removing infected plants (rogueing) also reduces virus spread. Monitoring and surveillance are used for early detection of the disease and vector, allowing timely intervention to minimize losses.