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Methods for Optimizing Seed Mortality Experiments

Published online by Cambridge University Press:  20 January 2017

Brian J. Schutte*
Affiliation:
United States Department of Agriculture–Agricultural Research Service, Global Change and Photosynthesis Research Unit, 1102 S. Goodwin Avenue, Urbana, IL 61801
Erin R. Haramoto
Affiliation:
United States Department of Agriculture–Agricultural Research Service, Global Change and Photosynthesis Research Unit, 1102 S. Goodwin Avenue, Urbana, IL 61801
Adam S. Davis
Affiliation:
United States Department of Agriculture–Agricultural Research Service, Global Change and Photosynthesis Research Unit, 1102 S. Goodwin Avenue, Urbana, IL 61801
*
Corresponding author's E-mail: [email protected].

Abstract

Experiments investigating mortality in the soil seedbank are aided by using only seeds that are initially viable and capable of remaining ungerminated (hereafter “persistent seeds”). However, seed mortality experiments often use heterogeneous populations containing persistent, nonviable, and germinable individuals. In this investigation we developed and compared nondestructive tests for isolating persistent seeds of two weed species characterized by physical seed dormancy (dormancy imposed by a water-impermeable seed coat): velvetleaf and ivyleaf morningglory. Individual seeds were weighed, steeped in water (hereafter “steepate”) for 48 h, and then assayed for imbibition. These seeds were then subjected to persistence assays conducted under controlled conditions (60 d in hydrated soil under 25/15 C day/night temperatures, 14-h photoperiod). Persistent seeds were less likely to imbibe and more likely to produce steepates with low electrical conductivity compared with germinable and nonviable seeds. For velvetleaf, persistent seeds were best segregated by comparing changes in steepate conductivity during 4 to 48 h of soaking, with the corresponding classification and regression tree (CART) model making few false discoveries (false discovery rate for persistence; FDRp = 8.6%, n = 93) and many true positive classifications (true positive rate for persistence; TPRp = 100%, n = 85). For ivyleaf morningglory, both a change in steepate conductivity from 4 to 48 h of soaking and imbibition status after soaking accurately separated persistent seeds (accuracy measures of corresponding CART models: FDRp = 5.6%, n = 150; TPRp = 100%, n = 142). Thus, for species with physical seed dormancy, we recommend use of steepate conductivity and imbibition status after soaking for isolation of persistent seeds. These seeds can then be used to optimize experiments on mortality in the soil seedbank. Nondestructive tests for isolating persistent seeds of species characterized by physiological seed dormancy require further research.

Los experimentos que investigan la mortalidad del banco de semillas en el suelo se ayudan utilizando solamente semillas que son inicialmente viables y capaces de permanecer sin germinar (de ahora en adelante “semillas persistentes”); sin embargo, los experimentos de mortalidad de semillas, frecuentemente utilizan poblaciones heterogéneas que contienen individuos persistentes, no viables y germinables. En esta investigación desarrollamos y comparamos pruebas no destructivas para aislar semillas persistentes en dos especies de malezas caracterizadas por latencia física de las semillas (latencia impuesta por una capa impermeable de la semilla): la Abutilon theophrasti Medicus ABUTH y la Ipomea hederacea Jacq. IPOHE. Semillas individuales se pesaron, se remojaron en agua (de ahora en adelante “el líquido de remojo”) por 48 horas y después fueron evaluadas para determinar su imbibición. Estas semillas fueron sometidas después a ensayos de persistencia llevados al cabo bajo condiciones controladas (60 días en suelo hidratado bajo temperaturas de 25/15 C día/noche y 14 h de foto-período). Las semillas persistentes demostraron ser menos susceptibles a absorber agua y más susceptibles a producir líquido de remojo con baja conductividad eléctrica, comparada con semillas germinables y no variables. Para la Abutilon theophrasti Medicus ABUTH, las semillas persistentes se segregaron mejor a través de comparar los cambio en la conductividad del líquido durante un período de 4 a 48 horas de remojo, con la clasificación correspondiente y el modelo de regresión CART, resultando en muy pocos descubrimientos falsos (taza de descubrimiento falso para la persistencia; FDRp = 8.6%, n = 93) y muchas clasificaciones verdaderas positivas (taza de positivos verdaderos para la persistencia; TPRp = 100%, n = 85). Para la Ipomea hederacea Jacq. IPOHE, tanto un cambio en la duración de la conductividad del liquido durante un período de 4 a 48 horas de remojo como un cambio en el nivel de imbibición después del remojo separó con exactitud las semillas persistentes. Las medidas de exactitud de los modelos CART correspondientes fueron: FDRp = 5.6%, n = 150; TPRp = 100%, n = 142. Por lo tanto, para especies con latencia física de la semilla, recomendamos el uso de la conductividad del líquido de remojo y el nivel de imbibición después del remojo para aislar las semillas persistentes. Estas semillas pueden ser utilizadas para optimizar los experimentos sobre la mortalidad en el banco de semillas en el suelo. Las pruebas no destructivas para el aislamiento de semillas persistentes en especies caracterizadas por latencia fisiológica, requieren de mayor investigación.

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Copyright
Copyright © Weed Science Society of America 

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