Asparagus is dioecious, which means male and female flowers are borne on different plants. In general, male plants have a number of advantages over the female plants. These include:

• Male plant lives longer than the female

• Male plant emerges earlier in spring than female

• Male plant does not produce fruits, which will compete with the crowns and roots for nutrients (Since asparagus plant depends on the nutrients stored in the crown and roots for next year harvest, reduction in stored nutrients will affect the yield and eventually the longevity of the plant).

• As male plants do not produce fruits that divert resources from the crowns and roots they out yield female plants over time. The yield advantage of an all-male field becomes increasingly apparent after the second or third year in production.

• Female plant has a tendency to lodge in heavy rain and strong wind as its fruits increase the weight of the plant. Male plant is less likely to lodge under the same conditions.

• Male plant has no seeds that can produce unwanted volunteer seedlings. Generally, volunteer seedlings are inferior to elite F1 hybrid and volunteer seedlings compete with F1 hybrid plants for nutrients.

Male asparagus is controlled by a dominant male (M) gene. Although male asparagus can be either heterozygous (Mm) or homozygous (MM), homozygous males rarely exist in nature. However, in rare situation homozygous (MM) male, which is also known as supermale, can be produced. The progeny of a heterozygous male segregates into males and females (1:1), whereas the progeny of a supermale consists of only males. Thus, supermale is the key to the production of all-male hybrids.

Male asparagus normally produces flowers with male organs as well as rudimentary female organs. Under certain growing conditions a low percentage of males may produce hermaphrodite flowers with functional male and female organs. Such flowers when pollinated will set fruits with viable seeds. Some of the seeds (~25%) will developed into supermale plants.

Another approach to produce homozygous males is by pollen or anther culture. Pollen will carry either a m (female) or a M gene. A pollen grain carrying the M gene can produce a haploid male plant, which can be induced by colchicine to convert to double haploid homozygous male.

Left: Male flower with fully developed anthers but rudimentary pistil

Right: Female flower with fully developed pistil but rudimentary anthers