Effect of Alternaria and Septoria spot on sunflower yield
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ORIGINAL PAPER
Effect of Alternaria and Septoria spot on sunflower yield Silvane Isabel Brand 1 & Arno Bernardo Heldwein 2 & Sidinei Zwick Radons 3 & Ivan Carlos Maldaner 4 & Fernando Dill Hinnah 5 & Fabrício Ivan Guse 6 & Jocélia Rosa da Silva 2 Received: 7 November 2019 / Revised: 19 August 2020 / Accepted: 23 August 2020 # ISB 2020
Abstract Leaf diseases affect crop yields. In sunflower crops, leaf spot severity can reach 100%, but the magnitude of the yield loss caused by the disease is not known. This study aimed to evaluate the effect of Alternaria and Septoria leaf spot severity on sunflower yield across different years in a humid subtropical climate. We conducted 37 experiments in Santa Maria, RS, Brazil, over 7 years. The hybrids Embrapa 122, Helio 358, Aguará 03, and Altis 99 were sowed and managed according to national crop recommendations. Severity assessments for Alternaria and Septoria spots were performed at 2- to 7-day intervals using a diagrammatic scale. We evaluated the effects of Alternaria and Septoria leaf spot severity on crop yield using upper limit graphs. The 37 experiments comprised 13 normal season crops (August to October) and 24 late season crops (November to February). The results were also classified according to the contemporaneous phases of the ENSO (El Niño Southern Oscillation): El Niño, La Niña, and Neutral. In normal season crops, severities of up to 24% do not result in yield decrease. After this, each 1% increment in disease severity produces a decrease of 66 kg ha−1 on sunflower yield. In late season crops, the reduction in productivity occurs at severities greater than 34%, with a decrease of 50 kg ha−1 for each 1% increase in combined disease severity. The highest severity values and lowest yields, both in the normal and late season crops, occurred in El Niño years. Keywords Septoria helianthi . Alternaria helianthi . Helianthus annuus . Severity . Production
Introduction Sunflower leaf diseases are mostly of fungal origin (Leite et al. 2005). In humid subtropical climates, Alternaria (Alternaria helianthi) and Septoria (Septoria helianthi) leaf spots are most common. Septoria leaf spot was first reported in 2007 in Rio Grande do Sul (Maldaner et al. 2009b), with high incidence and severe occurrences under some conditions (Maldaner
et al. 2009a; Radons 2010; Hinnah 2014; Brand et al. 2018). In a span of only a few years, it has become a cause of immense economic damage in the southern region of Brazil, due to humid climate conditions. As fungal pathosystems are favored by higher air humidity and leaf wetness (AGRIOS 2004; Leite and Amorim 2002a), these will have greater expression in rainy years. In addition, rainfall is a pathogen spore dispersion route (Amorim and
* Silvane Isabel Brand [email protected]
Jocélia Rosa da Silva [email protected]
Arno Bernardo Heldwein [email protected]
1
Universidade de São Paulo/Escola Superior de Agricultura “Luiz de Queiroz”, Piracicaba, SP, Brazil
Sidinei Zwick Radons [email protected]
2
Universidade F
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