Quick Methods to Estimate Seed Quality

Waiting for laboratory germination results to determine if seed lots require additional cleaning can be time consuming and expensive. The process can be shortened by making relatively accurate in-house measurements of seed quality. The Aberdeen Plant Materials Center (PMC) uses two simple procedures to estimate seed quality prior to sending seeds lots to a lab for testing, the pop test and historic bushel weights. A series of tests were conducted at the PMC to evaluate the accuracy of the pop test when compared with germination and tetrazolium results obtained from a certified lab. Popping reactions were observed and divided into three categories, 1) seeds that popped explosively and audibly, 2) seeds that rolled or moved but did not pop, and 3) no response. Means obtained from the pop test were used to create 90 and 95% confidence intervals (CI), and compared with results from the Idaho State Seed Lab. Our results indicate that the pop test is a good predictor of seed fill in newer lots of seed of many species tested. Combined pop and movement responses were well aligned with lab results. Lab tests fell within the 95% CI 15 of 30 times, and the 90% CI 25 of 30 times. Our results indicate that seed with any movement should be counted as viable, and not just those with a distinctive pop. Accuracy decreases with seed age, because seed embryos die at a quicker rate than seeds lose moisture. This paper also discusses the use of bushel weights to estimate seed quality and provides tables of historic seed bushel weights of several native range and pasture grass, forb and shrub species. Nomenclature: USDA-NRCS (2010) Introduction For certified seed production, seed samples must be sent to an accredited seed laboratory for purity, germination, and/or viability testing. Getting these results back may take weeks to months Figure 1. Hotplate mounted on a propane heater used for conducting "pop" tests at the Aberdeen Plant Materials Center. depending on the lab, time of year, and species being tested. There is also a chance that the lab results will indicate viability less than the standard required for seed certification, in which case the seed must be recleaned and samples resubmitted for further testing. This can be very time consuming and expensive. In order to expedite this process, the Aberdeen Plant Materials Center (PMC) uses a novel technique that allow them to estimate seed quality during the cleaning process and thus reduce the chance of not meeting seed certification standards. The “Pop” Test Healthy seed contains on average 12 to 15 percent moisture content at the end of the cleaning process. When placed over sufficient heat this water is converted to a gas, which exerts tremendous pressure against the seed coat causing an explosion. In the case of popcorn, as the gasses escape, the inner starch filled portions of the endosperm fill with air and expand into a tasty treat. A more practical (but less delicious) use of this phenomenon is to estimate seed quality before sending seed off to a lab for testing. The ability of seed to pop is dependent upon seed moisture content and the integrity of the seed coat. Even under good storage conditions, seeds lose this ability as the seed slowly loses moisture. In the case of popcorn, for example, optimum popping moisture content is approximately 14 percent. As the moisture content declines to below approximately 10 percent, popping performance goes down, and the number of unpopped kernels increases (Hamaker, 2010). Ogle and Cornforth (2000) compared “popping” results of 13 lots of eight native and introduced grass species with germination tests from the State Seed Laboratory and found a strong correlation between popped seed and overall viability. The trial presented here expands the list of species tested by showing results from 6 native grasses, 3 native grass-like wetland species, 3 native forbs, and 2 native shrubs (table 1). Materials and Methods The hot plate used for the popping test is a 1.6 mm (0.0625 in) sheet of steel welded with mounting brackets to sit over a heating element which is fueled with a 13.6 kg (30 lb) propane tank (figure 1). For best results we set the heater on high. Hot plate temperatures were determined using a Fluke® Ti20 thermal imager. Temperatures on the hot plate surface ranged