Development of a novel multivariate germination index to quantify seed hydration memory

In recent decades, the concept of memory has gained significant attention in plant ecophysiology research. When memory is expressed during germination, it is referred to as 'seed hydration memory'. Although numerous metrics relate to different aspects of germination, the literature lacks a method for quantifying seed hydration memory. This study aimed to develop a Germination Memory Index (GMI); a mathematical tool designed to quantify seed memory. The GMI enables comparisons of different native or cultivated species germinating under various conditions following discontinuous hydration. We tested the GMI using data from an experiment that evaluated germination of Cereus jamacaru seeds subjected to water deficit after undergoing hydration and dehydration cycles (HD cycles). The index is calculated as the arithmetic mean of gains, if any, in germination capacity, expressed as germinability, that is time to reach 50% germination, mean germination rate, uniformity of germination, synchrony and germination uncertainty, obtained from discontinuous hydration of the seeds. The memory ranges from 0 ≤ GMI ≤1. Gains are observed when HD cycles enhance germination capacity, germination rate and synchrony while reducing time to reach 50% germination, uniformity and uncertainty compared to their reference values. The absence of memory occurs when GMI ≤0, indicating that the germination process is favourable without undergoing HD cycles. When germination only occurs after discontinuous hydration, GMI = 1. Using the GMI, we can accurately measure gains in germinative behaviour provided by HD cycles, as this index reflects changes not only in germination capacity but also in germination time, speed, uniformity, synchrony and uncertainty.