Seed Vigor in Sweet Corn

 Gordon Johnson, Extension Ag Agent, Kent Co.; gcjohn@udel.edu

A common problem that occurs each year in the field is poor stands due to low seed vigor in a particular lot of sweet corn seed. By its nature, sweet corn has lower stored food reserves (carbohydrates in particular) compared to field corn. With the advent of different endosperm types than the traditional sugary (su) such as homozygous sugary enhanced (se), shrunken supersweets (sh2), and the more recent augmented shrunken types, vigor became even more of an issue. In general, vigor of sweet corn rated from highest to lowest is: normal sugary su > se heterozygous > se homozygous > sh2 augmented > shrunken sh2. Newer synergistic sweet gene varieties may have seed with vigor characteristics of a se or a su sweet corn depending on the specific genetics (check with your sweet corn seed company for specifics on the vigor of these hybrids). Supersweet hybrids (shrunken sh2) are noted for having inherently low seed vigor due to reduced food reserves and it has been a standard recommendation to plant these varieties only when soil temperatures are above 60 °F.

With the earliest sweet corn being planted now (end of March) in Delaware, seed vigor is critical, particularly if planting without the use of plastic mulches or clear covers. Choose types and hybrids within a type that have cold tolerance and make sure that you get seed lots that have good vigor. Your sweet corn seed supplier will have cold tolerance ratings of the hybrids that they sell. A good seed treatment package with appropriate fungicides and insecticides is also critical to obtain good early stands.

It is also a good idea to have the seed vigor tested if there is any doubt about the particular lot that you are planting or if you are considering planting carried-over seed. Factors such as growing conditions during seed development and maturation in the sweet corn seed production region, mechanical damage during harvest or cleaning, drying regime, seed conditioning procedure, and seed storage can have great impacts on the vigor of a specific seed lot.

The standard seed germination test is performed under ideal laboratory conditions (temperature and moisture). This will not reflect field conditions. The standard germination test is designed to determine the germination of a seed lot under ideal conditions, the highest germination potential. It does not help to evaluate the ability of a seed lot to perform under suboptimal field conditions.

Alternative tests that are used to evaluate seed vigor that are available from different state and private seed laboratories include:

The Cold Test – Seeds are germinated using a specific cold, moist treatment regime. This will be useful in selecting those lots that will perform the best under early cold soil conditions.

Seedling Vigor Classification Test (SVCT) – In this test seedlings from a normal germination test are rated visually according to vigor (strong or weak). Visual ratings are based on whether or not the seedlings have normal developmental characteristics.

Tetrazolium (TZ) Test – This is a quick biochemical test that essentially stains living tissue in a seed a red color. The more red staining, the more viable the seed.

Accelerated Aging Test (AAT) – In this test, seed is put under a high temperature and humidity regime for a period of time and then is evaluated using a standard germination test. This is often used to check the storability of seeds under less than ideal conditions but also will do a good job of evaluating seed vigor. Modifications to the Accelerated Aging Test have been made to do a better job of evaluating sweet corn types such as shrunken sh2 varieties.

The seed laboratory at the Delaware Department of Agriculture can perform cold germination tests on sweet corn seed lots that you want to have evaluated for vigor.

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