Foliage Plant Breeding
Although it has been stated many times that the breeding potential of foliage plants is very great, foliage breeding has not played a major role in the growth of the foliage industry or contributed many new varieties to the foliage market. Some notable exceptions include certain of the philodendrons aglaonemas and Christmas cactus. Foliage plani breeding is not easy and breeding programs take time, they take space and they require a knowledge of the breeding mechanisms of the plants under study. Anyone may be able to afford some time and space for a breeding program but will find it is almost impossible to find information regarding the breeding techniques of most foliage crops. This ' as well as future articles, will hopefully help anyone who has an interest in breeding foliage plants to develop an effective breeding program with a reasonable expenditure of time and space.
When selecting a crop for use in a breeding program, it is important first to choose one you like and have the capability of growing without a great deal of trouble. Two other factors should be considered when choosing a plant for breeding purposes. The plants must flower under your growing conditions and there should be a large selection of species or varieties available for you to work with and select from. These two factors serve as the cornerstone of any breeding program.
Breeding is selection. A plant breeder must select his crop, select the parent plants and finally select the outstanding seedlings. A combination of art and science is necessary to reach the final selection point. To be effective, selection must be carried out amopg a diversified group of plants or seedlings in a manner that the superior types are chosen. Superior choices must be based on the criteria determined by the person or persons making the selections. Needless to say, it is difficult to make selections within a single clone or variety as all those plants are identical. That is why a breeding program must be based on several different varieties or, more preferably, different species. The differing genetic makeup of each species may lead to new and possibly superior combinations in the offspring through sexual unions and recombinations. The greater the number of diverse plant types used as parents in a breeding program, the greater the chances of producing and selecting superior offspring.
The genetic differences contained in two different plants are combined through seed production resulting from planned pollinations. This can only be accomplished using plants which are in flower. Unfortunately, many types of foliage plants do not flower under Florida production conditions. The reason may be simply that stock plants are not allowed to reach the size necessary for flowering as they are continually being cut back to supply propagating stock. Several important types of foliage plants do flower under Florida conditions. Dieffenbachias, aglaonemas and philodendrons normally flower in the spring and early summer (April through July). However, a few of these plants may be seen flowering sporadically throughout the year. Aphelandras and fittonias flower at different times of the year while marantas tend to flower the year around except during the colder periods of January and February. The mechanism which causes these plants to flower is not known at this time, although the importance of being able to control flowering is apparent to anyone interested in breeding.
Flowers alone are not enough to ensure success of a breeding program. It is necessary to have a thorough understanding of floral structure in order to make pollinations. Individual flowers consist of
many parts which are listed in Figure 1. The two most important floral parts to the plant breeder are the anther and stigma. Anthers produce pollen, the dust-like substance used in pollinations. A pollination consists of collecting the pollen and transferring it to the surface of the stigma. The stigmatic surface is often sticky to the touch which facilitates holding the pollen in place. Unfortunately, the flower parts do not always appear as they do in Figure 1. The main key to identification is to look for pollen production from the anther. The anthers also may vary in number from one to several and they usually surround the stigma. Also, always attached to the base of the stigma is the ovary which will develop into the fruit following a successful pollination.
Just to complicate matters, some flowers lack various parts. Flowers which contain only male or female parts are termed unisexual. Both types of unisexual flowers may be on the same plant or on separate plants in which case there are male and female plants (hollies are an example). Foliage plants which have separate male and female flowers on the same plant include dieffenbachias, philodendrons and aglaonemas. These three types of plants have several male and female flowers clustered together on a single axis called the spadix. Male flowers are at the tip of the spadix and female flowers at the base. Other plants such as aphelandras, spathiphyllums, marantas, peperomias and anthuriums bear flowers which contain both male and female parts.
Another factor which may affect the success or failure of a pollination is the time at which a flower is pollinated. Normally, it is best to pollinate a flower the same day it opens as the stigma may not remain receptive to pollen for more than a few hours (possibly 1 to 2 days in some cases). Some plants, like certain of the philodendrons, only produce seed if pollinated near 2:00 a.m. Fortunately, this does not seem to be a widespread phenomenon among other foliage crops. The best time to pollinate any particular crop has to be determined by trial and error as it is currently unknown for most foliage crops.
All of the above factors are important in developing a foliage breeding program, Initially, it is important to choose a crop which will flower easily and collect as many different types as possible. Then, study the flower structure and learn when pollen is produced and how to make pollinations. Once this knowledge is secured, you are ready to begin the challenge and fun of foliage plant breeding.