Development of Starmaya

In 2001, a team of researchers from the French Agricultural Research Centre for International Development (CIRAD) noticed a tall-growing natural mutant of Coffea arabica called CIR-SM01 that did not produce any pollen (male-sterile).^[1] Male-sterile plants can be used as mother plants in breeding programs because breeders do not have to remove the male parts of the flower.^[11] Researchers verified the stability of the mutation causing male-sterility by cloning CIR-SM01 using somatic embryogenesis. They also verified that the mutation is a recessive trait, meaning both parents must have the trait in order for it to be expressed in offspring (this means that Starmaya is not a male-sterile plant, even though one of its parent plants is).^[1]

CIR-SM01 was then crossed with four different dwarf-type cultivars (Caturra red, Catuai 44, IAPAR59, and Marsellesa) used as pollen donors to test the possibility of producing F1 hybrid seeds.^[1] The researchers found that the cross between CIR-SM01 and Marsellesa (a variety also developed by CIRAD^[3]), which was eventually named Starmaya yielded 30% more green beans than the parent Marsellesa, with good beverage quality and also resistance to coffee leaf rust.

Cup quality

Beverage quality in the specialty coffee industry is determined by a protocol generally called cupping. This process evaluates a coffee on several different sensory descriptors including fragrance, flavor, aftertaste, acidity, body, balance, etc., rating each on a scale of 0–100.^[12] Any coffee rated 80 or above is considered specialty coffee. In the study, Starmaya received an overall rating of 82.5 compared to 83.13 for the parent plant Marsellesa and 82.9 for a control plant Caturra red.^[1]

Rust resistance

Coffee leaf rust is the most economically important diseases of coffee, worldwide.^[13][14] The most effective and durable strategy against CLR is the use of resistant cultivars.^[15][16] And while Starmaya was a proof of concept for mass production of F1 hybrid seeds, the researchers also evaluated its ability to resist rust infection.^[1]

One of the parent plants used in the study, Marsellesa, was observed in the field to be 1% susceptible to rust and the Starmaya plant was observed to be 8% susceptible.^[1] The researchers believe that Starmaya's resistance can be improved by first increasing the genetic fixedness (predictability of trait inheritance by progeny, i.e., a "fixed-line"^[17]) of Marsellesa. The high levels of rust incidence in Starmaya for this study were also partially attributed to alien pollination during the initial breeding trial.^[1]

Seed Garden

The seed garden was set up using CIR-SM01 as the male-sterile parent, or pollen receiver and Marsellesa as the intended pollen donor at a rate of 1:4 (receiver:donor). The planting density of the plot was 2 meters between rows and 1.5 meters between plants within the same row. This density allows for 4,000 trees per hectare. This configuration established efficient, natural pollination.^[18]

Seeds derived from the seed garden were successfully cultivated as F1 Hybrids, demonstrating that a seed garden is capable of producing F1 hybrids of this form at roughly half the cost of somatic embryogenesis.^{[19][Note 1]} It is estimated that a seed garden could effectively produce a half-million F1 hybrid seeds per hectare, per year.

The democratization of use of F1 hybrids becomes more realistic with the reduced cost and technical difficulties of using a seed garden to propagate F1 hybrids.^[1][18]