Systemic Acquired Resistance and Parson Brown Sweet Orange

Systemic Acquired Resistance and Parson Brown Sweet Orange

Parson Brown is a sweet orange variety that has been in Florida since the 1850s, originating as “a chance seedling at the home of Reverend N.L. Brown near Webster, Florida in 1856.” As the story goes, a hungry Brown found wild orange trees while lost along the Peace River in the 1840s. He brought home seeds from the delicious fruit and planted them. While Parson Brown oranges boast of having high amounts of juice with low acidity and sugar levels, the Hamlin has long been the favorite early sweet orange variety of growers due to traits like being seedless and more productive. However, that spot of favorite early sweet orange may soon be given to Parson Browns, as researchers believe the variety may have developed a systemic acquired resistance (SAR) to citrus greening.

 

Rediscovering Parson Brown Sweet Oranges

 

UF/IFAS horticultural researcher Manjul Dutt maintained that growers and others have noticed that Parson Brown sweet orange trees seem to be handling citrus greening better than their Hamlin competition. “Observations made in commercial blocks in Polk and neighboring counties illustrate an improved canopy density, improved mature fruit retention, and higher yields in the early-maturing Parson Brown sweet orange when compared to adjacent Hamlin blocks,” Dutt shared in a Citrus Industry article.

 

Researchers believe systemic acquired resistance (SAR) may be at work. “Preliminary molecular analysis of randomly sampled leaves from trees at a Lake Wales grove have indicated the possibility of systemic acquired resistance (SAR) playing a role in tolerance to HLB in the Parson Brown. Our current plan is to sample trees from all major citrus-producing counties to understand if this tolerance mechanism is prevalent in all clones of Parson Brown planted in Florida,” Dutt said.

 

SAR is basically when a plant develops its own responses to a pathogen, creating an immunity or resistance to the pathogen much like the human body will develop a resistance to a disease.

 

Dutt is leading a project looking into Parson Brown and a possible SAR response to citrus greening. The project is under consideration for funding by the Citrus Research and Development Foundation (CRDF). Dutt maintained “our current plan is to sample trees from all major citrus-producing counties to understand if this tolerance mechanism is prevalent in all clones of Parson Brown planted in Florida.”

 

While a SAR response in Parson Brown sweet oranges could lead to understanding how to transfer resistance to other citrus varieties, it could also make Parson Brown sweet oranges the favored early season orange variety. “Evidently with the terribly low availability of early processing fruit, the juice plants are more open to receiving Parson Brown than (they were) a few years ago,” shared Gary England, a retired Extension agent working on the project.