Aided by graduate student Robert Pyne, whose dissertation focused on developing genetic resistance in basil, the team found that commonly grown sweet basil (Ocimum basilicum) was far more susceptible than some of the other exotic, spice, and ornamental basils. In early field studies, all sweet basil varieties evaluated were found to be very susceptible to downy mildew. Other basil species and varieties with fewer symptoms include:
- ‘Red Leaf’
- ‘Red Rubin’
- Thai basil (‘Queenette’)
- lemon basil ‘Lemon’
- ‘Lemon Mrs. Burns’
- ‘Sweet Dani Lemon Basil’
- lime basil ‘Lime’
- spice types (‘Spice’, ‘Blue Spice’, ‘Blue Spice F1’, ‘Cinnamon’)
This suggests they may possess the genes for resistance to basil downy mildew, making them useful in a breeding program. Once resistance was identified in the other basil types, Simon and Pyne had to make hundreds of crosses to get the desired traits of sweet basil along with downy mildew resistance. This fine tuning is a craft in itself.
While developing a resistant basil is an accomplishment, Pyne points out “it has no commercial value unless it looks and tastes like a true sweet basil.” The team does their own informal quality assessments and they also provide samples to New Jersey and Florida basil growers to get important feedback. The breeding work is tedious, and promising varieties have to undergo further testing to see if they’ll hold up under extremely high disease pressure. In a university greenhouse screening room which was built to rapidly expose thousands of basils to this disease, the breeding lines are kept wet all day long in disease chambers.
A lot is riding on the success of the $1.8 million dollar USDA-Specialty Crop Research Initiative funded grant awarded to Simon and others in 2011. Sweet basil is the most commercially important annual culinary herb crop grown in the U.S. and one of the most popular garden herbs. Commercially, basil is grown for culinary use for both fresh and dry consumption and also to a limited extent is a commercial source of essential oil and oleoresin that are used in perfumes, food flavors, and aromatherapy products.