Growing Rare Fruit From Seed

John M. Riley

Seed Treatment Methods

Hot Water This treatment consists of soaking the seed in hot water for a period of time. One procedure is to pour boiling water over the seed, using about four volumes of water to one volume of seed. The intent is a thermal shock which rapidly diminished to room temperature. Usually this is followed by moist cold storage. Most pathogens are destroyed at about 160° F (71° C). The treatment is a little tricky for home use, since most seed are killed at 178° F (81° C). Sulfuric Acid Treatment The acid attacks cellulose and is often recommended as a dramatic treatment for seed coat modification. For the home gardener, handling sulfuric acid may present some hazard. Hydrogen Peroxide This is commonly available in a 3% solution. It may be used in full strength for about 20 minute to disinfect seed and alter the seed coat. The peroxide may then be diluted in half with water and the seed soaked for up to 24 hours. Sodium/Calcium Hypochlorite This material is commonly available as ordinary laundry bleach. It effectively sterilizes and disinfects when used in a 10% solution. This can be prepared by added 1/4 cup bleach to 2 cups of water. Soak the seed for 20 minutes to sterilize and rinse thoroughly afterwards. Alcohol and Other Solvents Many volatile solvents, including grain alcohol have been mentioned as having an effect on seed germination. Quite possibly this results from softening waxy compounds in the seed coat which are not water soluble. Gibberellin Gibberellic acid promotes germination in many seeds. It also helps overcome the tendency for some seedling to become dwarfed and to grow slowly after the harsh treatment used to initiate germination. Seed may be soaked with concentration of 100 to 1,000 ppm for 24 hours. Cytokinins Natural growth hormones stimulate the germination of many kinds of seed by acting at the molecular level on biological processes. Many synthetic cytokinins are available from tissue culture supply houses, but since they must be kept at a low temperature to prevent decomposition, they are not available in garden supply centers. Soaking for three minutes in kinetin at concentration of 100 ppm has been recommended. Ethylene This gas occurs naturally in plants and has a number of biological effects, including the stimulation of seed germination. One of the chemicals available to gardener to generate ethylene is ethephon. Since gibberellins, cytokinins and ethylene are three dominant components in initiating germination, it is natural that they work best when applied together. Potassium Nitrate Many freshly harvested dormant seeds germinate better if soaked in a 0.2% potassium nitrate solution. Seeds should be soaked for no more than 24 hours and then rinsed well. Thiourea This has been used to stimulate germination of some dormant seeds, particularly those that do not germinate in darkness or at high temperatures. A water solution of 0.5 to 4% is recommended. Since thiourea is somewhat inhibitory to growth, the seeds should be soaked no longer than 24 hours and then rinsed well. Vitamins The most common vitamin supplement for plants is vitamin B1 (thiamine). Other vitamins of the B complex are also useful. Nicotinic acid (niacin) and ascorbic acid (vitamin C) have all been recommended. Willow Tea A tea made from willow bark contains a substance that enhances the actions of plant hormones and appears to stimulate germination. Soaking seed in willow tea for 24 to 48 hours is suggested.

Procedures

Storage Life, in months, (assuming proper treatment) is listed in column two. The storage type (next column) is categorized as follows:

WTM--WARM TROPICAL MOIST Seed should be maintained above 70° F (21° C) and not allowed to dry out before planting. TI--TROPICAL INTERMEDIATE Seed should be dried to about 70% of harvest weight and stored a temperature of about 40° F (4° C). TD--TEMPERATE DRY Seed should be dried to below 50% of harvest weight and stored at room temperature or preferably 40° F (4° C). CM--COOL MOIST Store seed with sufficient moisture to prevent drying out at about 40° F (4° C).

Dormancy Breaker, column four, indicates any special treatment to break dormancy. In each case the seed can profit from a 24-hour soaking before planting.

SC--SCARIFICATION Seeds are made permeable to water by sanding, filing or nicking the seed coat. R--SEED COAT REMOVAL Carefully crack or remove outer seed coating. SK--PRESOAK Soak seed 24 hours before planting. MC--MOIST CHILLING After soaking 24 hours, pack the seed with moist sterile material and store for 30 to 60 days at 40° F (4° C). ST--STRATIFY Soak seed 24 hours and store moist for one or more seasons in the natural environment. Do not let seed dry out. WMS--WARM MOIST STORAGE After soaking 24 hours, store above 70° F (21° C). Plant soon. CW--ALTERNATE COLD/MOIST TREATMENT Soak seed for 24 hours and subject to periods of 40° F (4° C). Cycle several times if necessary.

Germination Period, column five, lists the time lapse between seedbed planting and emergence. Time required to break dormancy is not included. Times vary with cultivation and seed condition.

Hardiness (deg. F and C), column six. Values are approximate and are mostly taken from books which include the tropics, Florida and California. In a given situation, plant size, previous environment, health and chill factor can alter the response to a given temperature. There may also be significant differences in variants of the same species. The hardiness values listed are probably optimistic by about 5° F (2° C) for tropical fruit tree seedlings or young plants.

General Comments. A number following a symbol indicates the days of treatment required. A plus (+) after a number means the value may be exceeded. A temperature in parenthesis following the germination period indicates the minimum temperature (°F, °C) required for germination. The information on germination time is approximate and based largely on John Riley's personal experience.