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Ana Fita, Belén Picó, and Fernando Nuez

Roots are critical for plants to withstand environmental abiotic and biotic stresses. Wild taxa are often used as source of variation for improving root systems, as they are adapted to more stressful soil environments than their cultivated relatives. We studied the genetics of traits related to root biomass, root length, and root architecture (considering the primary/secondary and the tertiary root levels) in melon (Cucumis melo L.) in a 2-year assay by examining the root systems of mature plants in 91 F3 families derived from the cross between a wild accession, Pat 81 [C. melo ssp. agrestis (Naud) Pangalo], and a cultivated accession, `Piel de sapo' (C. melo ssp. melo L.). Despite the difficulties of working with adult plants, we found that Pat 81 and `Piel de sapo' differ greatly in their mature root systems, which is in concordance with the results previously obtained with young roots. Pat 81 developed roots with less biomass than `Piel de sapo', but this wild accession had more favorable root length and architectural traits: a higher density of framework roots, more uniformly distributed along the soil profile, longer laterals with a higher density of branches, and a higher number of root orders. This root structure is linked to a deeper rooting ability and to the capacity of exploiting a larger soil volume. The genetic analysis indicated that length and architectural traits are more stable than biomass traits, both between years and between developmental stages. Moderate to low broad- and narrow-sense heritabilites were found for root length and architectural traits, with most of the observed variation due to additive effects. Our results suggest that Pat 81 could be used as donor of valuable genes for increasing root length and improving the root architecture of cultivated melons, producing melons potentially more tolerant to soil stresses. The lack of phenotypic and genetic correlations between length and architectural parameters and root biomass suggest that root structure can be successfully improved without increasing carbon expenditures.

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Burton J. Hoyle

Soil particle size was found to affect expansion and contraction of soil mass as moisture changed; thus all other seedling emergence stresses changed. Cohesion between soil particles is changed by soil type, content, and particle size, which in turn changes seed energy requirements for survival and emergence. The rates of germinating/emerging; seed/seedlings accelerated or stopped depending on moisture fluctuations and water degradation of aggregates. The same moisture content may be damaging in one soil and not in another. Many seedlings with developed radicals and hypocotyls did not emerge and were found in pockets of fine soil below 0.5mm; or as if their energy had been used up. Stands after emergence frequently varied greatly in vigor and survival by many units. Vigorized seed produced variable results depending on soil stress limitations during emergence. That is, laboratory differences did not always reflect in the field. The least critical stress period was between planting and the emergence of the radical--about 1/3 of the emergence time. Ideal seed beds often produced poor stands when water management and temperature were stressful. Packing density was found a good measure of seed-bed soil quality.

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Rita de C.S. Dias, Belén Picó, Javier Herraiz, Amparo Espinós, and Fernando Nuez

Vine decline is limiting muskmelon production in many growing areas. Monosporascus cannonballus Pollack and Uecker and Acremonium cucurbitacearum Alfaro-García, W. Gams, and J. García-Jiménez are the main causal agents of this disease in Spain. The wild accession Pat81 (Cucumis melo subsp. agrestis Jeffrey) has shown to be highly resistant in naturally infested fields and after artificial inoculations. In three greenhouse experiments conducted over two seasons, the root structure of Pat81 was examined and compared to the highly susceptible commercial cultivar Amarillo Canario (AC). Pat81 produced a more vigorous, branched, and longer root system, conferring to this accession a higher capacity for the uptake of water and nutrients, even after inoculation using naturally infested soil. To determine the plasticity of the root systems, the effect of five different soil substrates on root growth was assayed. The root morphology was highly influenced by the soil substrate. Differences between genotypes appeared at 10 weeks after transplanting using sand as soil substrate. An organic substrate made up of well-decomposed peat and sand minimized the genotype × substrate interactions, and facilitated root analysis. This substrate allowed bringing the sampling date forward to flowering (at 7 weeks after transplanting). The maximum root length, the number and size of lateral roots (diameter 0.5-1 mm) and branching order, consistently differed between the two genotypes in most of the assayed substrates. These easily measurable root traits can be used as selection criteria in healthy soils to breed a larger root system more tolerant to stress. In addition, in inoculated soils the greater root absorbent area and the reduced lesion intensity of Pat81 could have applications to increase vine decline resistance of cultivated melons. By using segregant populations derived from the cross AC × Pat81, we are trying to modify the root structure of muskmelon in order to offer a genetic alternative to the expensive strategy of grafting muskmelon varieties onto rootstocks resistant to soil stresses.

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Ana Fita, Belén Picó, Antonio J. Monforte, and Fernando Nuez

to absorb water and nutrients, greater exposure to beneficial soil microorganisms, and a higher tolerance to biotic or abiotic soil stress ( Clarke and McCaig, 1993 ; Fita et al., 2007 ; Fitter, 2002 ; Lynch, 1995 ). The breeding of crops for

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Chun-qiong Huang, Guo-dao Liu, and Chang-jun Bai

Delhaize, E. Ryan, P.R. Randall, P.J. 1993 Aluminum tolerance in wheat ( Triticum aestivum L.). II. Aluminum stimulated excretion of malic acid from root apices Plant Physiol. 103 695 702 Duncan, R.R. Shuman, L.M. 1993 Acid soil stress response of

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Jun Yan, Jingbo Chen, Tingting Zhang, Jianxiu Liu, and Haibo Liu

.E. 2005 Aluminum tolerance of warm-season turfgrasses Inter. Turfgrass Soc. Res. J. 10 811 817 Duncan, R.R. Shuman, L.M. 1993 Acid soil stress response of zoysiagrass Intl. Turfgrass Soc. Res. J. 7 805 811 Eduardo, D.M. Willem, G.K. 2005 Long-term effects

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Azadeh Behrooz, Kourosh Vahdati, Farhad Rejali, Mahmoud Lotfi, Saadat Sarikhani, and Charles Leslie

alleviation of soil stresses. Vol. 1. Springer, New York, NY Romero-Perdomo, F. Abril, J. Camelo, M. Moreno-Galván, A. Pastrana, I. Rojas-Tapias, D. Bonilla, R. 2017 Azotobacter chroococcum as a potentially useful bacterial biofertilizer for cotton

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Carolyn F. Scagel, David R. Bryla, and Jungmin Lee

. 2014 Chapter 7: Salinity stress and arbuscular mycorrhizal symbiosis in plants. In: M. Miransari (ed.). Use of microbes for the alleviation of soil Stresses. Vol. 1. Springer Science and Business Media, NY Heidari, M. 2012 Effects if salinity stress on

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David M. Olszyk, Tamotsu Shiroyama, Jeffrey M. Novak, Keri B. Cantrell, Gilbert Sigua, Donald W. Watts, and Mark G. Johnson

(with S) maize cob biochar increased the concentrations of Fe, K, Mn, and Zn, and to a lesser extent, Mg and Ca (in one case biochar decreased Ca), in quinoa seed for plants growing under different soil stress conditions ( Ramzani et al., 2017 ). While