Researchers think Parson Brown may have a systemic plant defense (SAR) mechanism that makes it tolerant to HLB.

In the 15 years or so since citrus greening, also known as HLB, was discovered in Florida orange groves, many citrus trees have succumbed to the disease. However, many growers noticed that Parson Brown trees—an early season sweet orange that had fallen out of popularity when Hamlins arrived in the Florida citrus industry—seemed to display a tolerance to citrus greening. Researchers have been studying the variety, and they think it may have a systemic plant defense (SAR) mechanism that helps Parson Brown to tolerate citrus greening infection, according to a Citrus Industry article. See the details below.

A Systemic Plant Defense Mechanism

Parson Brown has been observed having “normal-sized fruit and very little fruit drop” and “enhanced growth and fruit-keeping quality” compared with nearby Hamlins and even when infected with citrus greening at the same rate as those nearby Hamlins.

Researchers looked at the RNA of Parson Brown trees, and they think they may have a systemic plant defense (SAR) mechanism that allows them to tolerate the HLB infection. According to the article, a SAR is an “internal mechanism that allows them to better protect against infection,” and “results through the movement of long-distance signals to and from the rootstocks to the scion through the graft union.” Research is continuing to identify how Parson Brown trees are able to better tolerate citrus greening and how that tolerance can be used to improve the Florida citrus industry.