Occurrence and distribution of soil Fusarium species under wheat crop in zero tillage

The presence of Fusarium species in cultivated soils is commonly associated with plant debris and plant roots. Fusarium species are also soil saprophytes. The aim of this study was to examine the occurrence and distribution of soil Fusarium spp. at different soil depths in a zero tillage system after the wheat was harvested. Soil samples were obtained at three depths (0-5 cm, 5-10 cm and 10-20 cm) from five crop rotations: I, conservationist agriculture (wheatsorghum- soybean); II, mixed agriculture/livestock with pastures, without using winter or summer forages (wheatsorghum- soybean-canola-pastures); III, winter agriculture in depth limited soils (wheat-canola-barley-late soybean); IV, mixed with annual forage (wheat-oat/Vicia-sunflower); V, intensive agriculture (wheat-barley-canola, with alternation of soybean or late soybean). One hundred twenty two isolates of Fusarium were obtained and identified as F. equiseti, F. merismoides, F. oxysporum, F. scirpi and F. solani. The most prevalent species was F. oxysporum, which was observed in all sequences and depths. The Tukey's test showed that the relative frequency of F. oxysporum under intensive agricultural management was higher than in mixed traditional ones. The first 5 cm of soil showed statistically significant differences (p = 0.05) with respect to 5-10 cm and 10-20 cm depths. The ANOVA test for the relative frequency of the other species as F. equiseti, F. merismoides, F. scirpi and F. solani, did not show statistically significant differences (p ≤ 0.05). We did not find significant differences (p ≤ 0.05) in the effect of crop rotations and depth on Shannon, Simpson indexes and species richness. Therefore we conclude that the different sequences and the sampling depth did not affect the alpha diversity of Fusarium community in this system.Instituto de Botánica "Dr. Carlos Spegazzini

Understanding first-year students’ curiosity and interest about physics : Lessons learned from the HOPE project

This paper focuses on results of an interview based survey of first-year university physics students, carried out within the EU Horizons in Physics Education (HOPE) project (http://hopenetwork.eu/). 94 interviews conducted in 13 universities have been analyzed to investigate the factors that inspire young people to study physics. In particular, the main motivational factor, which was proven to consist of personal interest and curiosity, was unfolded into different categories and detailed interest profiles were produced. The results are arguably useful to help academic curriculum developers and teaching personnel in physics departments to provide guidance to students in developing and focusing their interest towards specific sub-fields and/or to design targeted recruitment and outreach initiatives.Peer reviewe

Occurrence and distribution of soil Fusarium species under wheat crop in zero tillage

The presence of Fusarium species in cultivated soils is commonly associated with plant debris and plant roots. Fusarium species are also soil saprophytes. The aim of this study was to examine the occurrence and distribution of soil Fusarium spp. at different soil depths in a zero tillage system after the wheat was harvested. Soil samples were obtained at three depths (0-5 cm, 5-10 cm and 10-20 cm) from five crop rotations: I, conservationist agriculture (wheatsorghum- soybean); II, mixed agriculture/livestock with pastures, without using winter or summer forages (wheatsorghum- soybean-canola-pastures); III, winter agriculture in depth limited soils (wheat-canola-barley-late soybean); IV, mixed with annual forage (wheat-oat/Vicia-sunflower); V, intensive agriculture (wheat-barley-canola, with alternation of soybean or late soybean). One hundred twenty two isolates of Fusarium were obtained and identified as F. equiseti, F. merismoides, F. oxysporum, F. scirpi and F. solani. The most prevalent species was F. oxysporum, which was observed in all sequences and depths. The Tukey's test showed that the relative frequency of F. oxysporum under intensive agricultural management was higher than in mixed traditional ones. The first 5 cm of soil showed statistically significant differences (p = 0.05) with respect to 5-10 cm and 10-20 cm depths. The ANOVA test for the relative frequency of the other species as F. equiseti, F. merismoides, F. scirpi and F. solani, did not show statistically significant differences (p ≤ 0.05). We did not find significant differences (p ≤ 0.05) in the effect of crop rotations and depth on Shannon, Simpson indexes and species richness. Therefore we conclude that the different sequences and the sampling depth did not affect the alpha diversity of Fusarium community in this system.Instituto de Botánica "Dr. Carlos Spegazzini

Three Essays in Corporate Governance

Corporate governance issues have become increasingly important to financial managers and shareholders. Firms that are plagued by poor performance, incompetent managers, or excess agency costs have become the subject of a dramatic increase in shareholder activism. Dissident shareholders, who are unable to launch costly takeover bids or proxy contests, have initiated a process of governance reform through the use of shareholder sponsored proposals. Shareholder proposals are a direct attempt to reverse operating or voting policies, such as a proposal to repeal a classified board. Managers announce shareholder proposals in a proxy statement and typically include a vote recommendation against the proposal. In the first essay, I find an unfavorable stock price reaction to the announcement of a shareholder proposal. In some cases, however, management supports the proposal and negotiates an agreement with the proposing shareholder. Stock prices react favorably to a settlement announcement. If managers are willing to negotiate with shareholders, they are perceived to be acting in the best interest of shareholders. If managers are unwilling, shareholders believe a severe agency problem exists. In the second essay, the effect that ownership structure has on voting outcomes of shareholder proposals is examined. I find a direct relationship between the percentage of votes cast in favor of the proposal and levels of institutional ownership. There is an inverse relationship between the percentage of votes and managerial ownership and firm size. Large firms with powerful owner-managers present the greatest obstacle to the success of shareholder proposals. The repeal of shareholder rights plans is one of the most frequently used shareholder proposals. By adopting the rights plan, managers increase the probability of defeating a takeover, but increase their power in negotiating with a potential acquiring firm. In the third essay, I find that firms who combine a rights plan with high debt levels construct a powerful defense against a hostile takeover. Shareholders target these high debt firms and design proposals to repeal the rights plan