Exudate coloring test suitability for assessing the viability of coffee seeds ( Coffea arabica L.)

Abstract

-The exudate coloring test has been promising in order to quickly evaluate the quality of coffee seeds. The objective of the research was to adjust the coloring exudate test for coffee seeds and to evaluate the influence of the water content of seeds and of the imbibition period on the test results. Seeds from five lots of 'Catuaí 44' were used, with the following water contents: 30%, 20% and 12%. For the exudate coloring test, the parchment and silver skin (spermoderm) from the seeds were removed. Then, the seeds were distributed on a paper towel, moistened with water, and kept in a germinator at 25 °C for 24, 48, 72, 96 and 120 h. Four classes of coloring intensity were established: absence of color (A), light (L), medium (M) and strong (S) intensities, assigning the values 0, 3, 5 and 10 for each class, respectively. The Viability Index (VI) was calculated by the equation VI=100-(0xA)-(3xL)-(5xM)-(10xS). The exudate coloring test may be recommended to estimate the viability of coffee seeds, providing results correlated to the germination test. The best results were obtained for the seeds with 12% moisture content imbibed for 72, 96 and 120 h and seeds with 30% moisture content after 72 and 120 h of imbibition.

Water stress in germination, growth and development of coffee cultivars

“…In the laboratory, water stress can be simulated by the addition of osmotic agents in the seed substrate, such as polyethylene glycol 6000 (PEG 6000) solution. Hardegree and Emmerich (1994) found that physical contact between the seed surface of six grass cultivars and the PEG solution was sufficient to induce water stress in them. In addition, PEG 6000 has been used in germination studies since it is chemically inert and nontoxic to seeds; it simulates drought conditions; and it does not penetrate the seed coat, due to the size of its molecule (Ahmad et al, 2007;Almeida et al, 2014;Liu et al, 2017).…”

“…Plants subjected to lack of water may exhibit different models of perception of this stress factor, which may be modulated by the trait of drought tolerance belonging to each species. Individual cells of an organ under water restriction show changes in volume, accompanied by modifications in water and osmotic potential (Feng et al, 2016). The condition of lack of water at germination may delay primary root protrusion, reduce the percentage of seeds that complete the process, or completely inhibit germination (Velázquez-Márquez et al, 2015).…”