The two tycoons participated in a ribbon-cutting ceremony for new laboratories at the headquarters of the International Maize and Wheat Improvement Centre, known by its Spanish acronym CIMMYT.
The new complex will double the centre's capacity to develop better seeds and more productive farmers in the developing world, officials said.
"These laboratories will help attract the best talent in the world to come and work here," said Gates, founder of Microsoft and co-chair of the Bill and Melinda Gates Foundation.
Slim's charitable foundation donated $25-million to build the new complex, while the Gates foundation has given more than $90-million for ongoing CIMMYT projects, including an $18-million grant also announced on Wednesday to help boost small-farm yields in South Asia.
Slim and Gates are worth a combined $130-billion according to the ranking maintained by Forbes magazine.
"We have climate change but we also have significant volatility in raw materials, and that makes improved efficiency and farm productivity indispensable," said Slim, who controls a business empire that includes Latin America's biggest telecommunications company, America Movil.
Boost farmer profits
Mexico's agriculture minister, Enrique Martínez, told the assembled dignitaries that new advances in seeds developed by CIMMYT will help Mexico lessen its reliance on imported grains, especially corn.
Mexico currently imports about a third of the corn it needs each year.
More than two years ago Mexico's government began pumping resources into CIMMYT's sustainable agriculture programme known as MasAgro; $49-million since 2011 and another $138-million pledged over the next decade, according to data from the agriculture ministry.
The government says MasAgro, which has won plaudits from the G-20, boosts farmer profits by a third and yields by half.
According to the Mail & Guardian, Gates, with an endowment of R310-billion, now spends more on public health alone, at R16-billion a year, than the World Health Organisation's budget.
Ranked by Forbes as the world's fourth most powerful person, the Microsoft non-executive chairperson now measures profit in terms of deaths prevented, and his business plan includes the goal of saving the lives of eight million children by 2020, with a heavy investment in vaccines.
Gates now bankrolls so many organisations – from funding development journalism at Britain's Guardian newspaper to American schools and South Africa's Human Sciences Research Council – that the inside joke, according to leading philanthropy and social investment publication, Alliance magazine, is that "it's easier to list the organisations the foundation doesn't support". – Reuters.