Concentration Dependency and Stage of Crop Growth in Alfalfa Autotoxicity

Abstract

Shoots of alfalfa (Medicago sativa L.) contain water‐soluble chemical compounds which are autotoxic, i.e., inhibit the growth of alfalfa itself. The objectives of this study were to (i) determine the inhibition threshold of the water‐soluble chemical compounds (autotoxic principle), and (ii) demonstrate that the inhibition of seed germination on early seedling growth of alfalfa is due to autotoxinic compounds from alfalfa shoots and not from microbes. A farmer must make a decision on whether or not it would be advisable to replant alfalfa based on the level of alfalfa residue still growing in the field. Laboratory and greenhouse studies were conducted to determine if autotoxicity in alfalfa due to water‐soluble compounds is concentration dependent. Filter‐sterilized and non‐filter‐sterilized shoot aqueous extracts from vegetative and reproductive stages of ‘WL‐316’ alfalfa were assayed at 20, 40, 60, and 80 g L−1 (fresh shoot weight basis) for their effect on seed germination and root and shoot elongation of seedlings of WL‐316 alfalfa in a growth chamber. Compared with the control, root length, shoot length, and germination were inhibited beyond 20 g L−1 concentration. Shoot extract from the reproductive stage was more inhibitory than from the vegetative stage under laboratory conditions. In the greenhouse, incorporation of 4‐wk‐old green herbage from vegetative stage beyond 48 shoots per square meter level resulted in severe reductions in seedling emergence and plant fresh weight per unit area. Among the several phenolic compounds assayed for their phytotoxicity on root and shoot growth of alfalfa, coumarin and transcinnamic acid at 60 ± 10 μg mL−1 were the most inhibitory. Mixtures of five or more phenolic acids were more phytotoxic than their respective individual components except in the case of trans‐cinnamic acid and coumarin. Autotoxicity in alfalfa may be caused by an interaction of many, yet uncharacterized chemical compounds present in shoots.

Does Allelopathy Play a Role in Suppression of Mugwort (Artemisia vulgaris) by Alfalfa?

“…Thus, observations and data obtained indicated that AGAB may have some allelochemicals that are highly inhibitory on seed germination, sprouting of rhizome fragments and seedling growth of mugwort. The greater inhibitory effects of AGAB were also reported by other investigators (Chung and Miller, 1995c;Hedge and Miller, 1992). Increased amount of soil incorporated AGAB or AGAB extracts resulted in greater inhibition due to increased allelochemicals concentrations.…”

“…However, water-soluble allelochemicals such as saponins (Miller, 1983(Miller, , 1996Bialy et al, 1999), medicarpin (Dornbos et al, 1990), chlorogenic acid (Chung et al, 2000), and among the several phenolic compounds coumarin and trans-cinnamic acid were reported contributing to autotoxicity and/or allelopathy (Hedge and Miller, 1992). Alfalfa was also reported containing allelochemicals in all fresh or dry plant parts (Miller et al, 1988;Chung and Miller, 1995b;Miller, 1996), and such chemicals accumulate in the soil where the crops grown (Read and Jensen, 1989;Nelson, 1998, 2002).…”

Discovery and Weed Inhibition Effects of Coumarin as the Predominant Allelochemical of Yellow Sweetclover (Melilotus officinalis)

“…Imperatorin significantly reduced the root and shoot growth of lettuce at >100 μg mL -1 , and the effect on roots was more pronounced (Razavi, 2011). It was found that the root length of corn exponentially decreased with increasing coumarin concentration (Hegde and Miller, 1992). Furthermore, 10 -3 M of coumarin could significantly inhibited the root growth of alfalfa and barnyard grass with inhibition rates reaching more than 95% (Chon et al, 2002).…”

Evaluation of in vitro shoots of Artemisia judaica for allelopathic potential

“…These phenomena may account for the results obtained in the study with the extracts or powders of A. judaica. Su and Fang (1981) and Hegde and Miller (1992) also reported the adverse effects of phytotoxins from crop residues on the seedling growth of succeeding crops. The brown shoot extract was even more inhibitory to lettuce seed germination and growth than the green shoot extracts.…”